three things--
one, new boogies are brutally expensive compared to marshalls.
two, new boogies are pretty much the most complex tube amps ever made, so there's more things to go wrong. There's definitely something to the whole "floor model" thing because practically every Boogie I have played in my local store has SOMETHING wrong with it, but every fresh-out-of-the-box one has been perfect.
three, new boogies are wildly non-plug'n'play, and the versatility you get from them is frankly beyond most players' ears. My buddy and I, who are both pretty experienced tweakers, spent two hours dialing on a Roadster 2x12 in the store with one guitar and really only got one of the four channels to "OMG!!!!" and another to "wow, great tone." by contrast, you plug into an orange or a single-channel soldano and you have the one good sound it does right away. Even worse, you take a Line6, plug ANY guitar into it, and it sounds exactly like Linkin Park on an IPod-- so, must be good, right...?