the Deskpro team started working on all the consumer desktops

It's great news they decided to converge these products onto the same chassis, they are also doing the same on some notebook models as well.
The Presario mobo's are now designed by Compaq engineers too which is a welcome change. One I was looking at the other day had (paraphrasing a little here) "Designed by Compaq engineers in Houston, USA" silk screen printed on the topside - I sensed they took a lot of pride in having that on there and I wish them well!

the Compaq name will exist for desktops for a long time to come, to allow HP to have more shelf space at Best Buy and such

In addition, if HP dropped the Compaq brands (Evo, Presario, iPaq, Proliant etc.) then existing Compaq customers would perceive this as a change in supplier. The danger here is those customers would probably see this as a good time to put their business out for tender once again and HP would risk the chance of losing to Dell or IBM.