Trying, we do give a Birthday gift each to MIL & FIL. We only do "joint" gifts to them at Christmas, if it's something of a greater value, that is for both of their use.
I agree that it's expectations, because my Mom is painfully fair. She spends the same on her kids as her SIL/DIL, at birthdays and at Christmas. My Mom's fairness is legendary! My friends still laugh at the idea that when my Mom buys Christmas ornaments, she makes sure to get 2 similar ones, so that when she dies, we won't fight when we divide everything up.
With my IL's, the birthday gifts have been hit-or-miss. Sometimes they're good, sometimes they're just okay, but this is the 2nd time in 14 years that I've been missed completely. I even asked SIL if she and BIL got birthday gifts from the IL's, thinking perhaps the IL's had scaled back but not told us. But no, she said that they always get 'something'.
The first time they skipped my birthday, they actually sent a card, so I would know that they remembered my birthday, they just didn't get anything for me. This year too, they sent a text to DH's phone to wish me a Happy Birthday. The first time they skipped my birthday was pretty traumatizing to me, because that year I had personally picked out their gifts and went to a bit of trouble to do it too. That was the last time I had anything to do with their gifts, I've already left ALL of that (except the budget) up to DH. Even then, I sometimes can't help myself and will suggest things to him, because MIL is hard to buy for.
You know what's troubling me? I know that GMIL will receive her card and call MIL to talk about the pictures of DD, however MIL won't have received a card. MIL may even see the pictures on SIL's fridge. This will hurt her feelings. And I'm such a sucker that I feel bad about that. Maybe it's because I know that *I* will get blamed for it. But on the other hand, I've always left the card up to DH, maybe *this* is his way of "punishing" them? It's too many head-games for me!