HTC does that all the time.
Look at HTC's five WP7 phones for example. If you look and study them closely, look at their specs, they're pretty much face lifted HTC Desire, which is a face lift Google Nexus One.
The reason why HTC is so quick to the market with "another" phone, is that they take an existing phone and repackage it.
Note, the Droid Incredible is a repack of the Desire.
I said before, expect the Desire 2 to be a repackage of the MyTouch 4G. The Inspire and Thunderbolt are Desire HD repacks, in fact the Inspire uses the same case as the Desire HD.
The Incredible S is a bit of a surprise because it is GSM and it is using 4", a screen size that is not on any HTC before. It fits between 3.7" and 4.3" which I wonder why since it doesn't strongly differentiate from the other two.
The Wildfire S seems from the gene line that constantly reinvents itself as new since the HTC Magic. Then you got the HTC Hero, Tattoo, Legend, Aria, Gratia, Droid Eris and Wildfire and now this. Ditto with the Cha Cha. The lighted Facebook button is a reminder of the older days of HTC when you got lighted trackballs. The Salsa certainly screams "Legend" to me.
The Cha Cha phone with the Blackberry form factor seems interesting though. Note a resemblance to an early Android prototype.
Keep in mind, HTC is likely to have dual core phones based on the third generation Qualcomm Snapdragon possibly by summer.