Except that this doesn't really happen anymore unless the person's running an old version of Windows. IE updates with Windows Update, so it's just as "automatic" as Windows Updates.
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.
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.