Because that is the definition of obsolete? Check here, and here etc.

can't run the latest version of some software == obsolete
item suddenly loses all functionality == broken


An improved UI/UX is only one element that the end users consider. The perceived value of the handsets will also come from things like support. By closing the door on more complete OS upgrades for earlier handsets, they could relegate themselves to a second-class smartphone platform in the consumers' minds, they may see the options like this:

• iphone/iOS based - long term support for a few years, seen as an investment.
• heavily subsidised & budget handsets, WP based, unknown support, not seen as an investment, not a perceived safe purchase.

No, I think the only things that may help them do that are:

• the massive handset subsidies
• the MS cash reserves to allow them to continue the WP subsidies for years
• and the contract with Nokia to not make competing handsets.

more than the current quality of the WP handsets themselves.

Actually, the 3GS is upgradable to IOS6, please check here, and here.

Apple understands the two generations old 3GS is still for sale so they should probably support it for a while longer. Whereas MS knows the Lumia 800 and 900, and other WP handsets etc are the only options for sale, and announces non-continuation of support (on CURRENT flagship handsets)... the consumer will see a difference.

The 3GS will obviously not be able to run all software available due to hardware or imposed limitations, so it is also partially obsolete but nowhere near the extent of the latest WP farce. (i.e. there is no platform break/shift with the 3GS)... again, the consumer will see a difference.