As adults, we don't celebrate every birthday with a huge shindig the way we did when we were kids. Ask most moms what they did on their actual birthday and you'll probably get a list of chores, plus hopefully a nice dinner thrown in. But on those "significant" birthdays (things ending in 5's and 0's), we might do something a little more note-worthy, something a little more extravagant. But it seems so arbitrary.
Just as an aside to my beautiful, young, and vibrant sister: This is merely an example, and I am not insinuating that you are 49. However, to my brother that is 49: you are also
I'm so grateful my brother-in-law had the insight to throw a party in spite of the fact that this year isn't a nice round number. This year was an especially great time to celebrate her life.