That's true no doubt.He just doesn't want it to be widly known that he pays a lower percentage of his income than the average middleclass person.He's "hiding" something that isn't even illegal. Again, there's nothing wrong with that, but how would it look? AWKWARD.
It's also possible that there are one or two years where he really didn't pay any income taxes.
2007-2009 were pretty rough for anyone invested in the stock market and he could easily have had enough capital losses during those years to end up paying no taxes at all those years even though he would have had a comfortable income.
It's perfectly legitimate of course but it really doesn't work well in a campaign of 30 second sound bites.
Difficult to explain to the jobless masses.
If that's true, the decision to withhold those tax returns was a big mistake because it could have been overcome, but now it will linger on and on into the fall campaign and debates.