Why do speakers recommend amp wattage?

Probably because people expect it. In one sense it isn't very useful since size of room, average listening levels, type of music, ability of a given amp to driven a given load, as well as other factors play into how much power the amp should have. However, it gives you a general idea where to start. This is an area where there are so many variables that absolutes can't be given.

BTW that 80W is "power handling" which is different than recommended as it is the maximum they recommend. Probably the maximum continuous which is very different than the maximum peaks when playing music. Given their efficiency of 87 dB I think you would want an amp that is at least 80 watts and more wouldn't hurt.

You could put a kilowatt in front of your Ushers without fear as long as you were actually listening as you turned it up. Running at 'redline' for extended periods will probably result in some kind of meltdown, or ear damage!
Low power at too high a level is probably worse, as noted above.

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Tradition, I suspect. Often, the impedence curve is more important.

Nice thread. I was also curious about the wattage.

What is the importance of "current" in amperes? I have seen specs of amps with wattage but different current output. For eg. one amp had 200 Watts per channel and gave 60 amperes where as another gave 200 Watts but 45 amperes.

Thanks,

The most practical reason is as a guideline to avoid distortion and speaker damage due to clipping by running an amp with too little power too loudly.

In general, solid state amplifiers that deliver more current (amps) are able to better drive most dynamic speaker designs with varying impedance curves at various frequencies (referred to as a "difficult" load)and deliver more balanced sound from low to high frequencies.