Bitcoin is probably not a currency. It is however, a wonderfully efficient payment mechanism. So, when a large institution receives payment via Bitcoin, it's immediately converted into a stable unit of account, such as USD (typically via coinbase or bitpay). Similarly, when a company receives a warrant of payment from an American express customer, they convert that warrant into USD on a 7 day term.

As was mentioned elsewhere, when company ____ is announced that they are "accepting bitcoin", they are never actually accepting bitcoin. A payment processor is accepting bitcoin (and accepting the risk therein) and paying out in the businesses choice of currency.

Consider it similar to when you use a credit card in a foreign country -- you get charged in your currency, they receive payment in theirs.

Yep, they convert it all using a payment processor or keep a small percentage, no risk. State currencies are volatile too. Just look at the Euro.

Exactly. I would assume most using this strategy have the BTC payments converted to fiat at the time of purchase. Others might opt to keep it as BTC, which is fine and an assumed risk.

Yes. Whatever Bitcoin pay service the large institution uses usually assumes the volatility risk for a transaction fee and gives the recipient state currency.