Steve - I agree Apple make stuff which is better quality than a lot of IT stuff out there, but they don't have a monopoly on it.
Solid aluminium - this is common in the form of machined diecastings, and most upmarket laptops use this, or magnesium, or other stuff. My girlfriend has a stunning 2004 Sony laptop which is built from nickel loaded carbon fibre (current Sony stuff is largely crap though). The Ipad appears better built than most other £500 stuff, currently.
99% of malware comes not from software installs but from viruses people get over the internet, from emails especially if using Outlook, infected websites (including pilot forums
), bootleg software downloaded from P2P networks (P2P is flooded with trojans nowadays), and kids get malware transmitted over MSN chat, etc. Apple's control over the sale of application software does almost nothing to stop viruses.
Historically, Apple have been much less of a virus writing target because of Steve Jobs'
PR alignment with the widespread anti-Microsoft sentiment; whether this cosy situation will continue is anybody's guess looking at the growing anti-Apple sentiment over their Iphone 4 and more general signal strength indication cover-ups.
Long term, I see Apple having an ever bigger profile as a "big American corporation" and that will make them a target for malware written in China/Russia, and given the high correlation between being an Apple user and being non IT savvy, Apple users will be an easy target because while most serious PC users have effective AV software, most Apple users have no virus protection whatsoever.
Apple will pull an application from their store if they receive a complaint alleging some kind of legal issue. It is easy for one's competitor to make such an allegation.