I think everyone has nailed it on the head with increased control over all grain vs simplicity (and speed) when using extract. All grain is cheaper (for the ingredients), but there's increased equipment overhead initially.
Like @soccerdad, the main thing with extract for me is that I absolutely love being able to whip out a quick pale ale in an hour or two, so I've come full circle after starting with extract plus specialty grains, then moving to all grain, and then back...for some of my brews...I still bust out the full mash tun and do all grain at times as well, for more complicated brews that I want more control over, or that can't really be replicated with extracts well.
Like @soccerdad, the main thing with extract for me is that I absolutely love being able to whip out a quick pale ale in an hour or two, so I've come full circle after starting with extract plus specialty grains, then moving to all grain, and then back...for some of my brews...I still bust out the full mash tun and do all grain at times as well, for more complicated brews that I want more control over, or that can't really be replicated with extracts well.