This might be true. However you are taking a chance on whether or not your CPU will be supported.
1. Heat Issues. The heat sink for a laptop from from the laptop manufacture, not from Intel. The laptop manufacturer might of only made heat sink to support that one CPU.
2. Power Issues. The internal power supply is will only be geared for the the orginal CPU. A larger CPU might require more power
3. Motherboard Chipset Support. It might be the same socket. However will the motherboard chipset support the newer CPU. And there as been enough changes in the last few years to say that even if the CPU did fit, the motherboard chipset might not be support.
In the case of what technology has changed since the Pentium M days to the Current Core2Duo, there has been a lot of changes. I normally have a hard enough time trying to upgrade a 2+ year old deskcomputer which out changing a motherboard. It's more so with a laptop as you can not upgrade motherboards on laptops.
4. Motherboard BIOS Support. Some manufacturers only make the 1 laptop to fit the one CPU. They're might locked the BIOS so that it only takes the one CPU.
5. Finally, my favorite.... the cost of a Laptop CPU. Very expensive. With some of those prices just for the CPU, if you just double your money, you can start looking at purchasing a band new laptop.
Plus there is the other problem that i see. Upgrading a CPU to me is only worthwhile provided that you can get a 30% performance increase. Otherwise, it's not worth the time, money or effort.