In years gone by, the general public would've said exactly the same thing...how/where are they going to make up the performance gap? Surely, this is an impossible task.
No there have been loops holes, 6 wheels, fans, sideskirts, more recently f-duct they all get banned and similar ideas ruled out through regs, that stream of inventiveness gets harder and harder with each progressive regulation.
Then over the last 2 decades aero has been the main gain, but we are now approaching the last 1/10th of design. it's well understood and easy to extract the high 90% from the aero and costs millions and is very hard to find that last little bit.
other than the last few years, they have also been able to find time with engines both bhp and revs and things like the power curve.
all of these things will be outlawed in 2013, some have already been.