I don't believe this is quite right. If you mean "regular 401(k)" as a traditional one (i.e pre-tax), you are correct, but the original questioner (Stuffies12) did not mention a traditional IRA. Many plans allow after tax contributions as well. My understanding is that a taxpayer can move after-tax contributions to a 401(k) from that 401(k) to a Roth IRA tax free (known as a mega backdoor Roth IRA).
