Inflammatory title. Come on, seriously? The vast majority of people don't own iOS devices, but access the web through a variety of other OSs. Given that Android is outpacing iOS and that both are extremely popular, the Web is the obvious way to target both.
The Web is important because you can use it without regard for what type of computer you're using.
As I mention in my article, what you say is true, but hasn't stopped iOS apps from taking off. Yes, many people won't be able to use Mac OS App Store apps because they don't have Macs, but that won't be a problem to the web developers who switch to Mac, because they'll be willing to make the trade-off based on the hype and numbers that the Mac Store achieves.
Not everyone has a Mac, but enough people have one to make it worthwhile. And those Mac owners actually buy apps, unlike the vast majority of windows computer owners.
Most consumer windows PC owners pirate apps. Anecdotal evidence, of course, but for every one who's keen on paying for software there's 10 who will call a "techie" friend up and ask where they can get a free version.
If you have no real evidence for this assertion, then why do you even try to make the argument in the first place? Couldn't you just use that same logic for Mac users?
The Web is important because you can use it without regard for what type of computer you're using.