Well i think most of us haven't understood the OP's predicament.
His point is if AVR drives all 5 channels, then why is power mentioned in 2 ch driven and 1 ch driven - shouldn't it be 5 channel driven. The worry, i presume is, could this mean it drives only 2 channels?
I'll try to explain what i know - experts, pls chip in.
1. A 5.1 AVR drives 5 channels. There is amplification for all 5 channels.
2. At a given instance, movie tracks at the most have sound coming from 2 or 3 channels. Sound recorded into all 5 channels at the same instance, is very rare.
3. All said and done there is a number which is the total power output of AVR. That power is distributed to all 5 channels based on need (the track recorded into that channel). So at a given instance, if at the most 2 or 3 channels are driven simultaneously, what is the use of quoting power rating for all 5 channels driven at the same time - that is the logic of AVR makers.
4. This is actually a clever ploy by the manufacturers. It is a fact that if all 5 channels are driven at the same time, then power per channel will be a very small number. Not just that, most AVRs cannot operate at all by driving equal power into all 5 channels at the same time - they struggle and then go into "protection mode" (basically, shutdown).
5. As i said, in practice you will not get into situation (4) easily. Even if a movie scene had sound recorded into all 5 channels at the same instance, the power required to drive the speakers in the 5 channels will not be the same - ex: surround speaker may just need 10 watt and fronts may need 40 watt each for that instance.
6. Some reviewers actually test by driving all 5 channels simultaneously (ex: soundandvision.com avr reviews) and you find that only few receivers (expensive ones) even operate at that kind of load. See the review of my receiver Yamaha v473 here
Yamaha RX-V473 and RX-V573 A/V Receivers HT Labs Measures | Sound & Vision When all 5 channels are driven, it goes into protection mode.
7. Since most receivers are underpowered, some people who need real power go for dedicated power amplifiers like Emotiva XPA-5 along with their AVRs (or pre processors). The emotiva can easily drive good power into all 5 channels at the same time and can bring the best out of most demanding 5.1 HTs in the world.
Hope this helps and didn't confuse you even further