"When it comes to a ISP, why does it matter what OS I run?"

It makes no difference.

Let me use my ISP (Ignorant Service Provider) as an example - Clearwire.

CW, as an Employee explained to me, started up the Company great guns, got the money rolling, THEN FIRED ALL THE TECH STAFF.

The reason one gets an ignorant response to a technical question is that no one hires (or can afford to hire) competent people because they are EXPEN$IVE.

Its their JOB on the line, which is why they get defensive.They have cue cards and they read from them.

ISP Tech: "did you try rebooting the computer"

Me: "No, I just shoved a hot dog in the CD Rom drive and expected that to fix everything. Any more stupid questions?"