As providers we definitely never ask clients to verify BUT Its a statutory requirement in most states for the geteways to have verifiable Identity so their hands may also be tied by their regulator.
Most providers' TOS will state that they have to right to "withhold" an order and ask for further verification at any times (not limited to but a copy of your ID and/or front and back of the Credit Card used). Yet in most cases I just click "order now" and I am done.
To add the IRS also may ask the provider for the same AT ANY time so what different does a provider makes vs the gateway in that sense?