Planet have a pretty good way of going about it, releasing a new marker almost every 6 months which is very tempting for people who wont be able to sleep at night without owning the top dog gat.
Eg. Little Richard saves all his hard earned money that he scrounges of mum and dad and buys an SL74, happy as larry until today when pictures of the Ego8 flood the net and he must have it. suddenly the SL74 is old news and he decides to flog it at 3/4 of the price just to get rid and raise funds as well as the extra on the side in order to buy the 08 model
Then the process repeats when the 08 SL model is revealed and he must have it.
Personally I think planet have it sussed out but it is kinda annoying that my ego7 has dropped nearly 150 quid in value due to there already being 2 newer models out