estimated taxes

[Larmil]

This is probably because the IRS has no way of knowing which quarter the income was received without auditing the clients records.
I wouldn't be surprised if they find a way to do this in the future.

They already have a way. It is called Form 2210.

[veritas]

that's because

I would say he has been lucky.......

Suggest you hone your skills on preparing page four of Form 2210

FE

the IRS will not bother with the penalty if it is under a certain amount and the tax due is paid on time. They won't tell you what the amount is.