If it's legal to get on an installment plan and thereby use the money you hold back to make a bigger profit, why shouldn't a person do this? How is this any different from taking advantage of any other tax loophole? If there's something wrong with doing this intentionally (and I don't know that we have any evidence that those referred to in the OP are using this loophole), then the law should be changed to make it illegal.
Also, since the IRS charges an interest rate much higher than any of us can get in a secure investment, the "taxpayers" you refer to are actually receiving more, not less, in the long run.
Sounds like win-win to me.
You see wolf?? This is exactly the reason I'm so skeptical of 'owed back taxes' being an exceptional situation instead of some money making scheme.