You can pay Dell with bank transfer (they say "if you are ordering by phone or email", I don't know why not also when ordering via website too).   

But you are missing the point, it seems.  The question was whether merchants "accepting bitcoin" through Coinbase or BitPay are creating demand for bitcoin in the market (and thus contributing to raise the price); or, conversely, they increasing the supply (and thus lowering the price).

For people who have USD and no BTC, the bitcoin payment option offers no significant advantage over payment by direct USD bank transfer, since they would have to pay bank fees (and more) anyway.  Therefore those  "merchant adoptions" are not likely to motivate people to buy BTC.

On the other hand, those options are advantageous to people who own old coins, that were bought below market, because they provide a way to take their profits that saves some fees compared to selling the BTC at an exchange and then spending the USD.

I noted that the bitcoin option could be interesting for international payments.  However, Coinbase and Bitpay generally do not work across borders (not in the case of Dell, for example), so the point above remains.