However, most notebooks will indeed get annoyingly noisy if you do number crunching or something else running cpu at full tilt. And certainly, battery runtime is going to suffer a lot.
Notebooks usually have cooling systems with heatpipes, so the cooling area is actually quite large considering the size of the notebooks.
That said, I don't know why those dells throttle so much. Normal Speedstep certainly doesn't clock down that much, could be some serious thermal issue (if heatsink/pipe wouldn't make contact with cpu for instance), though I haven't read the pdf hence can't say if that's really an issue (there are tools out there to read out cpu temperature certainly...).