If considering wattage as in a solid state power amp, and not from tube guitar amps, then two 2x12's can sound the same as an equally powered 4x12 provided the drivers and cabs are the same. But, speaker impedance can be an issue. For a simple example, a 4x12 cab loaded with 16 ohm drivers is pretty common. These often have switches for mono 4 ohm, mono 16 ohm, and stereo 8 ohm - the last equates to a dual 2x12 setup using the same 16 ohm drivers.
If you drive this type of cab with a SS power amp capable of 250w/ch @ 8 ohm in stereo mode, it should sound exactly the same if driven by an amp producing 500w/ch @4ohm into the same cab in mono mode (Disregarding stereo FX). I definitely agree that much more SS power is needed to achieve the tube-like dynamics of the AxeFX. I had a Carvin DCM150 and it was not enough for a typical 2x12 or 4x12, compared to real tube heads. I'm now running a Crown XTi 1000 and I'm very pleased with it.