This argument is of course bollocks as well. If it were the only consideration then there would be no point in writing for other platforms. It's a sign to me that the company has mentally lazy management. It is of course also a variation on the "eat shit, millions of flies can't be wrong" argument.
Windows keeps me nicely in work. If I were designing for other platforms I'd have my job over much faster and I'd get less work because there would be little work to do[1], so I'm grateful to Bill for designing some really s**te software and selling it to large corporates.
Of course I don't actually use it myself, because I'm not as mad as a hatter and his hatstand.
[1] Not for the reasons you allude to, but for reasons that should scare the crap out of Windows users.