What do you base this bit of wisdom on, pray tell?
Sounds like the old "nobody wants to hack it because there's only 20 million (or whatever) machines out there" argument.
Which makes me wonder why there are viruses for freakin' CELL PHONES with 100k units out there?
cell phone viruses exploit elements common to groups of cell phones: the protocol used, bluetooth, etc... These things transcend the manufacturer.