while i agree, this only makes sense if you have an established brand. The iphone and ipad have this and i think the galaxy s line now do as well. But there is no way in hell HTC or Sony would simply add or remove some letters to their failing brand name for the next iteration of the phone if they wanted the market to notice it. Oh wait...
Its sort of a chicken and egg thing though. Maybe if they had stuck with one name (as Samsung has mostly done with Galaxy S), maybe they wouldn't be in the situation they are in now. It is much more effective to market one or two phones than to try and market 6 or 8. With one or two phones, the same marketing budget gets you much more bang for your buck because it doesn't need to be devided. This would also have built brand awareness. For example, in the early days of Android, the HTC Hero was one of the more popular phones world wide and had a reasonable good reputation. HTC didn't stick with that name, they switched to Desire, among others. If they were still using the Hero or Desire name, they would have been marketing the same name for 3 to 4 years now, and people would know and (likely) trust that name. People don't want to figure out the difference between an XV, VX, X, X+, XS, and whatever other confusing names they used. Now if they had the Desire (2012) as an entry/mid-range phone and an Incredible (2012) as the high end, they would have had several years of marketing and a trusted name bolstering them.
Plus if they had stuck with those two brand names, think of the marketing. Incredible. Desire. HTC. The names play so well together you could EASILY market them both in one commercial.