So, it both sucks that your 40th didn't get the attention you'd like, and I'd add to those above who've suggested that the mostly likely reason is something other than 'they love my brother more than me'.
Esp. if it's ben a few years, they may have a change in financial status, health, mental focus, energy, etc. In fact, I'd suggest that the $200 gift is a powerful sign that they didn't feel up for doing something more-thoughtful - cash is always nice, but it's also to some extent a 'gift of last resort', when you can't do something better.
Honestly, I'd take this as an opportunity to take a good hard look at what's going on with them - I'd be surprised if a bit of investigating didn't turn up something significant going on with them that you haven't known about.
Your behavior angers God and/or the Constitution. Just sayin'.
I only seem liberal because I believe hurricanes are caused by low barometric pressure, and not gay marriage.