Microsoft calls this stuff "crapware". Unfortunately many OEMs are paid good money to put it on there and sometimes use it to subsidy the materials cost.
I think Microsoft should put the hammer down personally but can't see it happening at the moment.
This is the thing - I can't even begin to quantify how much damage the crapware does to the interface and general user experience. Toolbars taking up half the screen, floating 'media controls', links to trailware splattered all over the desktop, pre-installed antivirus mithering you to purchase the full version, half-baked backup and recovery programs, 'wireless assistant' software which makes it more difficult to get connected.
Unfortunately this is the experience for lots of people who buy a computer. The price we pay for cheaper machines I suppose.