It's simpler for non-experts to change the postfix configuration than to change the sendmail configuration. So, why shouldn't he not suggest it?
because it's stupid, lazy advice.
1: it's easy for non-experts to edit the sendmail configuration too... as long as they're editing the mc file, not the cf.
2: changing software doesn't help solve the problem.
3: what if he has a bunch of milters or related programs that rely on sendmail? are they all available for postfix? what needs to be changed to match his current environment? have you thought about that? has anyone asked James that before recommending he changes his software?