There are a lot of things you can do with a DSLR that P&S cameras can't, change lenses, external flash, cable release, depth of field preview, the infamous BULB setting - great for lightning pictures. and so on
Cameras like the Canon G9/G10/G11 is a totally different animal as a normal P&S and shouldn't be put in the same category; it's more or a hybrid. This Canon series of glorified P&S cameras can use an external flash, cable release, depth of field preview (press button half-way). ...it's digital screen even has over twice the pixels of the $7,000 Canon EOS 1DS Mark III (230K vs. 461K pixels), or if you like a manual viewfinder it has one which even has diopter adjustment.
Yes, they don't have a bulb setting, but if 15 seconds isn't enough you might just be doing something wrong (or taking pictures of stars under a cloudy sky or something).
Changing lenses also isn't a problem for 99% of people since they want to lug a single camera around, and not a camera bag. The zoom of 28-210mm (if my memory serves), and with a great macro mode, will serve most people very well. There are collars to attach various macro, zoom, and fish-eye lenses which actually do a decent job, but the trade off is it makes the camera nearly the same size as a SLR, and just isn't worth it to me.
Shutter lag is still something I don't like with a little over a third of a second, but if you're pre-focused (shutter button held half way), it's extremely fast at 0.072 seconds says one review of the G11 (I know my G9 is a bit slower).
To end my little Canon "G" series rant, I just wanted to say that I started off with a very nice SLR back in the day (and before that an ancient, all manual Exacta), and even borrowed a nice $3K DSLR for a couple week vacation, and it's just not worth the hassle to carry around a huge camera bag with multiple lenses when I want to enjoy my vacation with the camera simply fitting in my pocket. If you're a pro doing photoshoots then sure, you would use a proper DSLR/medium format/whatever, but P&S's have come a huge way recently and for my casual (and a little bit of use for shoots for my graphic design business), this is all I really need.