The simple answer to that is actually another question.....Do you have music that plays down to 10hz, or even below 20hz? Chances are good the answer to both is No (unless you listen to a ton of classical), in which case having flat response down that low isn't an issue.......I.E. 20hz is "good enough". And just as an FYI, that sub rating of 10hz is pretty much meaningless.
But, back to the topic.......an amplifier's rated frequency response doesn't mean the amp just stops playing below that point. It doesn't play 20hz, but output nothing when given a 19hz signal. The response is (typically) a rating of where the amplifier's response has ceased being flat and has rolled off by some arbitrary decibel level. It's arbitrary because there's no industry standard for how to "rate" the frequency response. One amp may rate the frequency response to -1db, while another may rate it to -10db. So without knowing what criteria were used to derive the measurement for both amplifiers, you really can't cross-compare them.
So, really, the short answer here is that no, it's not important.
