i dont know about that... if the density is 40GB and the speed is 5400RPM, then it should have similar STR characteristics as a desktop drive of the same platter capacity...
The only diff I can think of is that the platters are smaller in a laptop drive and thus, probably are more similar to a short-stroked drive that has a single 60GB platter but is capped at 40GB.
Of course, we are just talking about STR here... seek times are horrid on laptop drives... low heat, low noise, low power, lower cost... these are the things that make them attractive for laptops, but at the cost of slower performance.