You will not see a bunch of accessories for a device like the Eris pop up the day the phone comes out or even in the first month. The companies that usually make accessories get access to the phones about the same time that we do, so they take a little time to come out. The stuff that Verizon is offering were commissioned by Verizon I am sure. So those manufacturers had access to the phone a little early.
Keep in mind that the Eris is on one carrier in one country. Phones like the Curve, iPhone, Storm, Treo, Hero (original) etc are typically available on many carriers in many countries and the accessory market is much bigger. The iPhone is actually a unique accessory whore unto itself and we will probably never see the same volume of accessories for any other device. There are accessories out there for the Eris and more will come out as demand arises, but right now the demand really isn't there. If you think about it from a manufacturing stand point, why would you make anything? You would be making a bunch of items that a smaller group of people may or may not buy. Not a very sound investment really. Especially when you can make the same thing for the iPhone and most likely sell at least enough to cover the cost. Top all that off with the fact that HTC isn't really in the accessory business and you can begin to see the problem. Like I said, there is stuff out there. The following list took me all of 3 minutes to find and I really didn't look all that hard.
Case
Car Mount
Case
Screen protector
Desk Charger
Case
Skins
Pouch
Charger Combo
Case + Car Charger
Case/Charger Combo
Case Charger Combo
Stylus
Case
Case
Stylus
Leather Case
Combo Charger
Leather Case
Skin Case
Skin Case
Skin Case
Skin Case
Skin Case
Car Mount
Leather Pouch
Stylus
Car Mount
Leather Pouch
Car Mount
Extended Battery (kinda)
Desktop Charger