[acdha]

Which is still slower: making the assumption that automatic updates are actually enabled (which is often not the case), Microsoft's update cycle is slower (monthly) whereas Chrome & Firefox have both deployed patches within a day of learning about a new zero-day. Microsoft also does not update Flash (prior to Windows 8) or blacklist known-insecure plugins as quickly – better than in the past, to be sure, but still concerning as the reaction loop speeds up.

[zanny]

And the important part is that Microsoft rapidly depreciates updates on old versions of Windows all the time. The adoption of Windows 7 in the poweruser space is probably significantly higher than the adoption in the grandparents category of people still running 2003 - 2004 Dells with XP. Most of them, if unassisted by more tech savvy relatives, would still be running IE 6 - 8, and 9+ won't be backported. Throw Firefox or Chrome on those old PCs and they will stay auto-updated forever.