Well, its the battery technology.
Dell tries too hard to minimize their prices and they forget to take safety into account.
When you're building hardware around something as dangerous as a Li-Ion battery, you should really be a little more concerned about the quality of your product.
I also think it has alot to do with companies trying to pack too much power into laptops. I really don't think that laptops need to be as powerful as they are - at least not until the manufacturers can find a way to keep them under control. If you seriously need that much power, you should just stick to desktop computers. IMHO.