They have their uses…
For the typical consumer who simply buys a computer and treats it like a non-upgradeable appliance, there's little difference. Laptops have the benefit of being easily transported. The downside is they cost more to repair and purchase.
For the more technical users, I think it's more than just gamers. I bought my current desktop with the view of it lasting the next 5+ years. (1 down, 4+ to go.) I'm yet to see a 6-core laptop with 2×1TB disk space in mirror RAID on the market.
On the other hand, I do have a laptop … I can take a laptop (or three) on my bicycle to work without any problem (okay, a little sweat), the sight of a full-tower desktop and a 20" Sun GDM5410 bouncing down the road in a bicycle trailer is just a little too heartbreaking to imagine, not to mention hernia inducing.