First (and of course I didn't bother to spend the five minutes to look it up), how recent are those purchases? If they're fairly new, their new parent companies may not have finished an overhaul yet. Google has done that before — taken the foundation built by companies they purchased, worked on improvements internally, and eventually deployed the Google-flavoured version. It is only sensible to keep running the lesser product in the meantime.
That's the first and easiest interjection out of the way.
Secondly, I think you're putting too much emphasis on the tech reporters and alphageeks, here. Sure, they were important in getting the word out, but Google and Yahoo have grown a huge reputation by now (heck, the names permeate everyday life, no mean feat), and probably don't face an uphill battle at all to get the word out about new products. Sure, it's a nice bonus if the tech reporters pick up on it, and it might sour a few of the more “fastidious” to hear the tech reporters saying it won't work on alternative platforms, but that really doesn't make much difference to the “masses”. (Cf. Windows, Internet Explorer.)
Third, at least Google does offer one product which remains Windows-only: their Googlebar. Worse, it's IE-only. There is an open source clone for Mozilla that works on any system the browser runs on, but of course it's not endorsed. The question here is, how much loss does this annoying narrowmindedness really incur? One can only speculate.
I don't know.
I wish the tech reporters and alphageeks really had as much influence as you're assuming here, but I've gotten too cynical to really believe they do.