If you don't see that that's fine ....
You sound very defensive about this, which leads to the flip side of your argument: any prospect who can't take the lightest of jabs at their pet platform is not a person many "high level" startups would be interested in at all.
I understand you are making an app on iOS though and it would be perfectly legitimate for you to have constraints on employee setups because of that. But for a company working on a RoR project where the window manager doesn't matter, who seem to be having trouble recruiting, I'd suggest the data here clearly indicates they should drop the phrase as there is no way (looking at those numbers) it is helping them filter out some trouble making characters with a bad attitude towards Apple, it's turning a huge number of people off. And as I said elsewhere, there are companies certainly paying more and certainly working on more interesting problems who don't do this.
It makes sense to standardize and to have a reason if you want to deviate (said from the perspective of someone that would want to deviate). However, I'd still reword it if I were them, based on this reaction.
Even PG's Lisp versus Blub argument is tenuous. Languages and OSes are a dime a dozen. What matters are algorithms and real world results. If you don't see that that's fine, but some real machine learning company thinking at the level of algorithms and not tools will eventually come along and eat your (company provided) lunch.