Sure it's a marketing slogan. I suspect many folks who use IE are unaware of the alternatives.
But the question wasn't about whether there are alternatives and the alternative you are recommending just isn't significantly better in this regard (Chrome is far better than Firefox for this, which leaks memory like a sieve).
I really hate IE, it adds about 10% more work for most of my web development and by all means I'd love for people to stop using it. But if I went to a mechanic to ask about a problem with a Hyundai I wouldn't want his only answer to be that Honda is better and I shouldn't use a Hyundai. It may even be right and even be useful information in some contexts but it doesn't fix the problem, and if the user was asking about Firefox crashing you'd not be telling them to switch to IE.
Essentially the "use a Mac" and "use Firefox" is just "use what I use" in lieu of a real answer and it's a pet peeve of mine to see so many simple questions being answered with someone's browser preference instead. Answers should be cross-browser too.