The idea that elevated feeders might decrease the risk of dogs suffering bloat was never anything more than a popular theory - which, once finally tested by veterinary research in the late 1990s, was found to be false. Not just false in terms that raising feeding bowls fail to reduce the risk, but that it actually increases the risk by over 100% (and that finding has been re-confirmed by successive studies). Since bloat is fatal for nearly half of all sufferers, and boxers are reasonably high on the risk list in the first place - it really doesn't make a lot of sense to use them. The dog is perfectly well capable of reaching his bowl unaided, and need do so only for a matter of minutes, if not seconds, daily.
There is a sticky thread at the top of the health forum with information and links to bloat research.