I genuinely don't know if I'm being a massive bitch. 
For starters we're all Americans and I know that long distances to you wouldn't seem quite so massive to us, so that may come into play. :) But.
My parents live about 300 miles from us. Takes five hours in the car on a good day. We have three kids (9, 3, 1) so it always takes considerably longer given bathroom stops etc.
DH works 8-6 Monday-Friday. I stay at home and do part time child minding during the school year and don't drive. 
(I really need to learn and stop being so afraid!) My parents are 56 but my mother is frequently not in fantastic health. She has chronic migraines and thyroid issues and has to get cortisone shots in her knee every few months. :( She works from home and is pretty flexible. My dad also owns his own business but works ib a hardware store on the side. (His business has been slow lately so he's picked up more shifts at the store, too)
Anyway. My DC are the only grandchildren on my side and seem likely to remain so, at least for years. My mom talks a lot about us moving closer but seems to have accepted that won't happen. She's talked a lot about moving closer to us but my dad REALLY doesn't want to. She still talks about it but I don't know how serious it is. She looks at houses occasionally but she admits that if it weren't for us, she would never think of leaving. I would like them closer but it's a lot of pressure for my family to be her only reason for being in a certain place. I would feel like we had to be around every time she wanted to stop by and also like we couldn't move if we ever wanted to. (I don't think we ever will, but who knows.)
They see the kids pretty often. They are really good about coming down and staying if I have a meeting or even a doctor's appointment or something. I NEVER make them feel obligated too but they always offer.
They often have the older two for long weekends at theirs.(Maybe every six weeks or so?) Usually we meet them halfway and drop off the kids. Sometimes they will bring them all the way back and sometimes we meet again. We don't often go all the way to theirs...maybe just a few times a year and then we stay in our family's lake cabin. The reason we don't is that our house is a fixer upper and there's always SOME project or another going. Plus DH and I rarely get to go out together so we use the time the kids are at my parents' to work on house stuff and/or occasionally go see an actual movie that doesn't have cartoon characters in it. :) My mom wasn't fussed about seeing me all that often before I had the kids (we get along well but she's pretty clear on the real draw being the DC) so I never think it's all that important that DH and I go up there.
This weekend is a long one (Labor Day here on Monday) and then DS starts school on Tuesday. A few days ago I was telling my mother that as it's the long weekend I was going to get a babysitter to be with the kids so I could finish the project I'm working on (switching some bedrooms around including repainting and ripping up carpet) because I want the boys to be settled in their new room before school starts. She texted "well you know you can drop them here anytime" and I didn't say anything... probably sent a smiley or something.
Today she brought up the weekend again and suddenly started in on how we never "just drop them off, you only bring them all the way here if you're going to stay at the cabin." I explained that that probably wouldn't happen because DH wouldn't be able to get there before midnight on a Friday night with them and then he would have to come right back on Sunday to get them. She just said "yep, I know" in a tone that implied she and my dad are always doing that very thing. Which isn't entirely true, they never take them just for a few days because it's not worth it with the driving. It's usually a four day weekend at least.
She said she was telling my dad how we NEVER just "drop them off" and he agreed and was angry about it.
I don't know if I'm BU or not but honestly I can't see that we are ever going to do that. I don't drive but even if (when, hopefully) I get my license I can't see driving five hours at night on a Friday and dropping them off and then leaving. If DH or I bring them up there we will stay for the weekend and then come home all together.
She got off the phone kind of quickly after that and I'm not really sure what to make of it all. My dad will drive down to drop the kids off or pick them up and then drive back a few hours later, but I always tell him it's madness and he should at least stay the night. He doesn't usually want to though. Once they drove down and stayed for six hours to see DS's school concert and then drove back home. I have never asked them to do any of this and I always try to get them to stay. We don't have a lot of room but they could sleep on our bed or the couches, but they never want to. My dad has talked about putting a guest room in our garage (he's a carpenter of sorts) and maybe then they would.
I don't want to make it sound like "if you don't pick them up halfway you won't see them as often" but to put it bluntly that's kind of the way of it. DH can't take his whole weekend driving there and back and there and back again and we can't always get away for an entire weekend to stay up there (we have a massive dog too and no one to watch him when we leave so we have to take him with us and he doesn't get on well with my parents' dogs). We could probably make it up every 2-3 months as a family and stay for a weekend but I know she will complain about going that long and also not seeing them "all to herself."
AIBU to say that we are never going to just "drop them off"? Sorry this is so long.