What I find odd is a lot of MILs seem to think that DILs have "stolen" their son away
This is exactly how my MIL behaved. FIL not only taught my MIL that the world should revolve around him/them but also taught her that everyone who marries into the family is a threat to their happiness. Once you realise that this type of IL has a totally different way of viewing family, that you begin to 'get' the way they think. These are people who don't see their adult offspring marrying as a sign of life moving on, being pleased that their children are happy etc, as normal families do, with these ILs, their children's partners are seen as a threat. What my DH was to his parents was the provider of their happiness and taxi service; he had a 'use' to them that made them happy and he wasn't seen as a person in his own right. They thought that because they were happy, then he was happy too and he'd want to do that for ever more. It didn't figure in their minds that he might want more in life and that he might want to do that 'grown up' thing of getting married. Once they realised that they were going to have to tolerate me, they 'trained' him through their tantrums, that they should come first and to be very afraid of upsetting them, no matter what the affect on our family (DH, me and DDs.)
As an aside to this MIL/DIL thread, I learnt several years ago that it isn't just me that the ILs haven't got on with. My MIL had a sister and it's often been said that her and MIL (and then FIL) were very close. This sister used to drive the ILs around as well and when she got married a few years after the ILs did, they say they didn't get on with him because (in their words), "he was a weird Irish bloke." And when DH's sister got married (several years before I came along), it's said that FIL took 8 years to "get used" to BIL being there! So I guess the signs of what DH's parents were going to be like, were there long before I came along. Add to that, that the ILs have no friends or hobbies and even though they live in the same town as their other relatives, they never see them, it all kind of adds up to a weird way of thinking when it comes to family and to life in general.