"high-priced Unix boxes" Same tired old argument. As many have said before, compare like with like and you'll find very little difference in price. Sure you can go into PC World and buy a laptop for £300, but it'll be of very little value except as a paper weight to anyone in the real world.

Lack of "app software"? Like what?

As for security, at present (and I emphasise 'present') there are no exploits which can lead to control or infection of standard Macs out in the wild. Yes there are reports of vulns but still no reports of actual living hacks by oriental miscreants or otherwise gaining access to Macs via the interweb.

Seems to me a safe bet so far by the military...