I think I remember someone else having a similar problem where they couldn't shift thier Rocket's tranny, and if I remember correctly it turned out to be a loose shift fork on a shift shaft that was the culprit. There is a bolt that locks the fork into place and the bolt backed out for whatever reason. I don't know if this is what has happened to your bike but it sounds somewhat similar. I really haven't heard of this happening very often (you can search through our forums here to see), I believe BigErn's bike had a similar problem but the root cause of his problem was that he dropped his bike and bent the shifter shaft that enters through the side of the engine case.
Hopefully the guys at your dealer will get it sorted out. Its unfortunate that it had to happen, I guess the true mark of a good manufacturer is what kind of service they give you when a problem arises. I would almost have to believe that those bolts securing the shift forks would be on the list of quality control checks to make sure they are torqued correctly, but you never know when a piece of metal has some sort of internal flaw that rears its ugly head later down the road.
I work for Nissan, which has a reputation along with Toyota and Honda for being a quality car company, and we have problems like these from time to time. Nothing is perfect, that's why there are warranties. If you want to see bad build quality.... check out the parts return bin at any Hyundai dealership, there will be at least 10 junk trannys added to it every week along with heads and blocks and just about everything else. In comparison Triumph is a shining star...
I may be lucky but other than some squeaky front rotors (which cured itself) I haven't had a lick of trouble with my Rocket in 2 1/2 years of ownership...