Rightly or wrongly, manufacturers including kite companies generally don't have an interest in maintaining second hand values on their products unless there is money to be made in selling the products and services to keep them going. Whatever you think of North, I think they deserve some credit for providing a good range of spares for new and older models - this is true in the UK at least. Managing to keep a single bar working for all kites for the last 4 years is pretty good too. I don't agree that North stuff has a poor resale value either, I've sold a few old kites recently and the second hand market seems pretty good right now if you're selling a well known brand.
Related to this - one thing that's just appeared recently in the UK is North dealers offering generous trade-ins on 06/7/8 vegases - send an old one in, any condition, and get a new 09 for reduced price. The question is why and where are the kites going? The only conclusion I can make is that they want the old ones off the second hand market to maintain the value of the 09 and presumable '10 models. Is this happening anywhere else?
http://www.brackleshamboardriders.co.uk/?p=332
re: updating models each year, again its no different to any other manufacturer - a kite co. wants to be seen to be offering an improvement (whether it really is or not) or some kind of innovation each year. If they don't then people complain that they aren't doing anything new - not sure you can keep everyone pleased.
I agree about the confusion over which kite does what - I heard the Rhino has been dropped and the Rebel is being pushed into the racing/speed/big air slot while I guess the Evo will be the freeride/wave kite...? yes i know it's marketing spiel. Depends how much you want to keep up with the latest latest. Personally I wait until this time during the year and try and pick up new or lightly used gear from the previous year or year before, capitalising on the dealers wish to shift old stock and the people desperate to have this year's badge on their kit.