Is it actually normal to have some checks for this now? When this happened a few years ago in Australia the apnic writeup (someone has linked below) essentially said there was no scalable solution yet.
in an ideal world that has not existed for over a decade, IRR data could be used to automagically generate accurate prefix lists but for all the usual reasons (inaccurate, stale data; obtuse interface; etc) that just isn't done on a wide scale.
You can put a prefix limit on a session (that's the "little" in little to no) but that doesn't stop someone from announcing 10,000 more specific routes to popular (YouTube, Facebook, Twitter, Akamai) destinations.