Hi Nelly,
I honestly wouldn't worry too much about quoted frequency responses of loudspeakers, in reality there are so many factors as to how your system will sound. You rarely hear the lowest notes in "normal" music and just because a speaker may reach 30Hz at +/- 3dB there's nothing to say it won't have a very strong midband or treble which on balance could make the speaker sound lightweight.
Your room is also a huge factor in the sound - I had some pre-production prototype speakers at home a few weeks back and they measured up in the midrange by about 2-3dB on our reference samples, in my room however they sounded far too bassy (and this was a small speaker) purely due to the nature of the room and the positioning. After I'd blocked the ports they sounded fairly balanced but if I were to take them back to the office and measure like that they would look to have very weak bass!
I'd say by and large to ignore pretty much all the figures you see on speakers within reason, find a shortlist of those you think suit what you're after (including looks and size you could live with) and have a demo, preferably in a room/system similar to yours and if at all possible even try at home.