NanaNina I've often thought (and continue to think) that I wish to God that you were my MIL. Honestly. Every line oozes with love for your dgc - and your ds and dil. It's palpable and, fwiw, I'm very, very jealous that you obviously have such a wonderful relationship.
But, sadly, not everyone is the same.
I've had 15 years of my mil (and fil, to a greater or lesser extent) putting DH down, making it very clear that he is second best (he has one older brother), and that I am useful for nothing more than incubating a child.
I was told at 17 that it was pointless continuing with my education and that we should get married and provide them with grandchildren. Yes, that was 15 years ago and these comments started within 3 weeks of us starting dating.
Now that I'm pg with dc1, I have never, ever seen them (mil especially) so excited. When we got married they were barely interested. In fact they caused DH (and I) a huge amount of heartache. Tomorrow we are going over there for Sunday lunch - they invited us "just becausethey would like to see us" - for the first time in EIGHT YEARS. Suddenly they have a reason to want to know us, rather than put us down and show no interest in our lives whatsoever. The vast majority of invites we have extended to them - coffee visits/dinner/even staying with us so that travel to see MIL's elderly mother would be slightly easier - all rebuffed. Mostly without reason - just a flat "no thank you".
Example - DH was made redundant 2 years ago. Mil made it quite clear that she was disinterested because her PFB "might" be made redundant in the following few months.
Another example - mil sat in our garden, on DH's birthday, eating our food and drinking our wine, loudly declaring that a mother's first born is always their favourite and that it can't be helped
DH is 4 years younger than BIL. She also openly says that she was so disappointed that DH was a boy that they considered adopting a girl 
What I'm trying to say (not very succinctly) is that not everyone is the same. I wish to God I had a good relationship with my ILs, and DH and I have both tried to have a good relationship with them but in vain. We repeatedly lead the horse to water but they won't even take a sip.
I do find it hurtful that people say that MIL's are bashed unfairly on here. Any group bashing at all isn't on, but I think people forget that it isn't a case of targeting a particular group. Each thread that is started is generally as a result of a problem in a relationship. Now that could be a problem with a DP/DH/brother/sister/IL/the visiting Martian from up the road. It doesn't matter. Yes, some posts are pretty unreasonable, but surely the point of MN is to offer advice and support - not to bollock posters for having the gall to have a problem in a particular relationship.