Dell have been doing this for a long time. The last three laptops that I've brought from them have all been 10/100 on machines that would benefit from a faster network connection. My Vostro 1500 "Small business" notebook only had a 10/100 connection. It was a bit sad that the wireless interface was the fastest network interface on the laptop.
More annoyingly, what is now my main machine which was the dell laptop that was on here in the deals section also only has a 10/100 interface (and had a low spec wireless card as well). Intel I7, high definition touchscreen, 16GB Ram, had a 1TB hybrid SSD drive, but dell saddle it with a 10/100 network interface. I've replaced the wireless card so I can now do sustained 30MB/S transfers, however, for the rest of the spec of the machine, 10/100 really is pathetic.
I suspect, as others have suggested, that Dell are trying to push people to their more expensive business machines.