Having owned budgies and bourkes, I can tell you that they are not that similar at all! Budgies chew a lot, are "friendly" to the point of being annoying (i.e. very 'in your face' kind of attitude), more aggressive, more chattery, more excitable, etc. Bourkes are more laid back and calm. Budgies typically enjoy head scritches, either from other birds or perhaps from humans. Bourkes, generally speaking, don't enjoy them.
I don't think many grass parakeets actually enjoy allo-preening, which might be the reason why they aren't considered to be good 'pets'. The more a parrot enjoys allo-preening (in the wild), the more hands on they are (within captivity). Cockatoos are at the other end of the spectrum. They love it! You can pet them all over and they'd enjoy every moment of it! Most other species at least enjoy head scratches, and some, like conures and macaws, may also enjoy petting in areas other than the head, but usually not so much as a cockatoo. (not to say that it's a good idea to pet anywhere other than the head!)