Android phones, apps and tablets

Yeah, but over time phones lose support for OS upgrades and get worse at running newer apps, whilst networks push the cycle by offering upgrades to get people to renew contracts. On the other hand DSLRs have standard lens systems, meaning the user can upgrade their camera to a certain extent for a long time after the model is originally released.
Also don't DSLRs hold their resale value much better?

OS upgrades don't stop the phone working (unless they're Vodafone ones.. ;)), new apps might not run as well, but you bought the phone to use the apps available now not 2 year's time. In theory, new apps should run better due to better code (in practise they'll bloat). If they're not supported by the device they won't be available to download anyway so users will be unaware until their annoying compulsive upgrader mates tell 'em.

10Ds are £200 on ebay. I'm not sure what the UK price is but it cost me $3000 when I bought it many moons ago.