I meant what was his justification for it

the same could be said of those with visual/aural impairments.
I see that now -I misread- and wasn't agreeing with the statement

.
I don't dismiss developing for Linux/Mac browsers, just for me they come lower in my list of priorities and I generally lump them just above edge-cases. In an accessibility audit I'd generally go Core browsers > Search Engines > Impaired Users > Browsers on 'fringe' operating systems (like Fx on Linux or Mac, and Safari).
I work on 'assumed' compatibility and accept the minor differences caused by the host OS. Gecko, Presto and Webkit should behave similarly enough across operating systems and devices, regardless of the host browser, to be safe only checking on one OS i.e. Windows if that's your primary platform.
Of course, if you have the time, a thorough check is a great idea.
Where did I say that? In fact, I said you must check for Mac browsers as they tend to be demographically important (they have money) and shout loudly (fanboys!) when sites don't work.
With Linux users, they tend to be tech-savvy and are prepared to install multiple browsers particularly Firefox and so far we've never identified any significant difference between Firefox versions or OSes.
Unless it's for an Intranet with therefore a single browser/OS combination, not checking browser compatibility is commercially deficient.
Ah, my apologies. I assumed sarcasm where there wasn't any -that's my own opinion coming into play

. Those are fair points, and I think it's certainly worthwhile ensuring there's an acceptable experience in those browsers. But still, I've not seen significant enough usage to make them
priority browsers for development. 10,000 IE users spending £5 beats 100 Safari users spending £10, and the average consumer isn't likely to be reading TechCrunch or Slashdot.
Having said that, Safari
is a browser I'm more inclined to check properly (I'm required to at work!), but I don't lose that much sleep over it. Incidentally, does anyone know the split of Safari vs. Firefox users on OSX? I thought most Mac users have ditched Safari in favour of Firefox. I'm happy to be enlightened!