While it isn't a big deal, I felt the same way as the OP when I bought my first BMW. Whenever I had to take my car in for service at lexus, I ALWAYS got a new model lexus loaner. Not sure if BMW dealers are too cheap to provide enough BMW loaner cars or if BMW's just have way more problems than Lexus.
They used to give out loaners for routine oil changes without more than a day's notice.