I think it's shades of grey, and a couple of posters have summed it up very well in that we have years to learn our own Mother's ways, and we (hopefully) won't make the same mistakes when we are MIL because we went through it 
that said, I do agree that DH's family is me and DS, and by that I don't mean that he should sever all contact with his parents, but that we are his priority now not his Mum/other family members
Actually, I am the one that has reestablished his relationship with FIL as he was too afraid of MIL reaction without my support... but that's my own issue/my mental MIL
They can't call around without an invite - No, I don't want ANYONE dropping by unannouced staying until they feel it's time to leave and disregarding my/our wishes for privacy. This applies to everyone, My mother and his. Just because your child lives there does not mean you have a right to call in whenever and for however long you please - people have lives and routines FFS
They can't pick the baby up without permission - No, not if you're trying to create a rountine and they're disturbing it, or are taking the child away from Mum without asking, especially in the early days.
In my case, MIL invited herself round as soon as I was released from hospital after a long an traumatic labour, took the baby out of my arms and demanded I make tea/cook while she and DH bonded with the baby 
They can't buy the dcs presents because it's just 'junk' that 'clutters up the house'.
To be fair, I think this is a GP issue as opposed to a MIL one, but again, yes if the childs parents are setting reasonable boundires for gifts then no you can't buy crap lots of gifts
They can't ask to take the baby for a walk because that's 'taking over'
It depends on the context, if Mum is frazzled and needs a break then go for it, if it's actually time the parents want/need to be spending with their DC then no.
I think another poster said it, but most MIL have some trouble realising that they are not the centre of their Son/GC's world and can tread on toes because they want to re-establish their bond OVER the bond between the DH/DC and DIL
So you are being a bit U, but there are also some silly MIL bashing diva's out there
Read a lot on here about posters being reduced to tears by their MILs (sometimes understandably) but I wonder how many MILs go home in tears because yet another well meant gesture has been thrown back in their faces, or they have been made to feel like they have no right to a special relationship with their grandchildren?
Yes, GP's do have a right, but within the context of respecting the parents choices and recognising they are the primary carer and not using it as an excuse to undermine the childs parents