There may be something to that, especially with the fact the Obama campaign is paying huge amount$ for staff, etc. They're burning money like there's no tomorrow.
We may be seeing a "rope-a-dope" strategy unfolding here, because on balance, Romney hasn't been badly damaged by the onslaught by the Obama campaign. While Romney closes the gap in the cash-on-hand department (if he hasn't already drawn even), it appears he's marshalling resources until after the convention, at which point he'll bombard the airwaves when voters begin more intensely focusing on the election. It'll be a reverse of what Obama did to a resource-poor McCain in the waning weeks in '08.
In other words, Romney may be laying low for a reason, wait until end of summer, after the convention to begin to POUNCE.