My take is that the bike has had a modest increase in popularity recently, due to fuel prices and its having been publicly touted for its fuel mileage and appeal to entry-level buyers in a few magazines. I don't think it could be considered as "selling like hotcakes" but demand appears to be up considerably compared to past years.
Tdubs come 2 to a crate. Typically dealers buy a crate for the new model year and never replenish because replenishment means having 2 examples what have traditionally been slow-selling, low demand bikes on the floor.
Anyway, that's my take. The demand for smaller bikes in general is on the uptick, but maybe not quite to the degree that dealers are willing to commit advance orders on them. This has affected the used market as well. Any TW that rolls is worth considerably more than it was a couple of years ago.
If this is a real trend, in this economy dealers probably will need to watch the market until they've seen enough customers simply leave the building when they can't find what they want and can no longer be sucked into a spendier or sportier model as they have in the past.