seidio has an established track record for expediting product development for some phones over others. the evo had a lot of hype and therefore seems to be getting the most attention for now.
for example even though the incredible has been out longer...the evo cases were ready at almost the same time the phone was released and there's a larger selection while incredible owners waited, the evo has a dock already and the incredible doesn't, there are media cables for the evo and none for the incredible...it's actually a pretty long list.