Stevenknapp, my 2610 has the 2. 2GB hard disc, or I believe they call it a microprocessor, with all the USA maps in it. You can add this to the 2610, which makes it the same as the 2620. I never have to load anything from my PC again.
You can get a large compact flash card for the 2610, yes. You had to hook it to your PC at least once tho right? The advantage of the 2620 is that it comes all in one. No PC needed, not even once. And the disk drive is sealed in the unit. Otherwise the units are identical. And Garmin sells both.
I don't know about on trucks, but the vibrations having it mounted on a motorcycle have caused a number of 2620's to fail. The 2610 with a large flash memory card, not hard disk, is the most robust way to go IMHO.
FWIW, it's not called a microprocessor, that's a different thing. Compact Flash or "microdrive" would be the two common terms for the memory used in the 2610. Heck, if you ever needed more storage, or the card broke you could replace it. Can't do that on the 2620.