Microsoft is accepting the US dollar, not Bitcoin.

That's silly. That's like saying any brick and mortar small business doesn't accept "credit" because they use a payment processor to process their credit cards. Or that places on the Canadian border don't "accept Canadian currency" because it's immediately exchanged for USD. The fact that not-Microsoft is processing the payment in bitcoins and exchanging it into the currency that Microsoft wants doesn't mean that you can't buy the intended good from Microsoft with bitcoins.

Yours is a reasonable analogy and it works and it's a good point; it doesn't counter the parent comment IMO.

A small business won't accept credit because of the risk, so a third-party will pay the business - for a fee - and take the risk of the credit themselves. The business isn't accepting credit as you point out.

Here MS aren't accepting bitcoins they're accepting the use of a third-party that will pay them in dollars on your behalf.

What's the point of that distinction? Well if MS truly accept bitcoins themselves then they would have holdings in bitcoins rather than in dollars, they would then be [capable of] trading in bitcoin and would legitimise it somewhat. Here they're not legitimising it to any useful degree, they're allowing BitPay to do all the bitcoin elements.

tl;dr - Call me when MS \buy\ something using bitcoins.

companies such as MS want to get involved in bitcoin however they need regulatory clarity to do so. By using BitPay they get to be involved with a modicum of insulation from unclear regulations. I would expect that MS are not taking all of the payment in $ but are keeping some in BTC.

What is meant by "Microsoft accepting bitcoin" is that you can buy things from Microsoft using bitcoin. Customers don't care about the details of currency exchange on the back-end.

Bitcoin seems unstoppable at this point.