Are you sure? E.g. AT&T in the list seems to accept via bitpay, does that really mean that AT&T has it's own bitcoin wallet where they receive the btc? (I do not know, but I just have some doubts)
Further, what percentage of those companies will continue to "accept" bitcoin if they are no more allowed to convert them to dollars?
Almost all companies will sell the Bitcoin as soon as it's paid, yes, most without ever touching it themselves. It's just like using a credit card as far as they're concerned. See this chart from BitPay on how they work: https://support.bitpay.com/hc/article_attachments/3600338995...
Remember that every actual Bitcoin transaction requires, on average, paying a $17 transaction fee to pay all the miners and the electricity they used in processing the transaction, so you don't want to actually be sending it between people often.
I have mainly used Namecheap and NewEgg, not AT&T. Many of these companies may not process Bitcoin transactions themselves, but instead rely on a third party like Coinbase/Bitpay who handle the BTC-to-fiat conversion, so in that case the companies would not themselves host a wallet. My "directly" I mean that you don't need to convert your BTC to fiat to pay for these services. I suspect that most of the companies would stop accepting Bitcoin if it couldn't be converted to dollars, but that's not what I was replying to; I specifically said that "prices are pegged to fiat".
Further, what percentage of those companies will continue to "accept" bitcoin if they are no more allowed to convert them to dollars?