For some reason I was thinking app... but the issue is the same for web:
For a website that uses a CC to purchase a product, the user is going to have to enter their email address as there needs to be some way to communicate to them. So the difference is now entering a password. Is that really more work than reading some text about making a decision of creating an account vs. checking out as guest?
I (unfortunately) buy a ton of crap on the internet and I can't remember the last time I saw a "Checkout as guest" option. Can someone point me to a site or two that does that well?