Technology turnover - how often do you really have to upgrade?

I like tech gadgets, I really do. The idea that in my hand I can hold a device (my Nokia N95) that is several orders of magnitude more powerful and can store more data than the entire computing setup I grew up with (TRS-80 + 5.25" Floppy drive) is pretty mind boggling when you sit down and think about it. When I was younger, Dad had one of the first mobile phones I'd ever seen in person - and it was only "mobile" in the sense that it was hard wired to a car..... "DAAAAD - your car's ringing!" (Mrrmm... 'horn alert')

Looking at the progression from there to now, however, I do wonder whether perhaps we too rapidly deprecate equipment before its useful life is expended.

Let's look at two specific examples...