That is definitely a contributing factor. If I give my employer a DCC receipt and the amount is in GBP, I get refunded the exact amount in GBP. If I give my employer a receipt in any other currency, I get refunded in GBP at some dodgy* exchange rate my employer has created.

My credit card doesn't have one, but my employer doesn't refund non-sterling fees charged by banks, so going DCC is actually better for most people at my company.

* = After querying this with our finance people, it is apparently calculated as the average interbank exchange rate for every day in the previous month, i.e. nothing like the rate you actually paid.