I'm sorry, I'm not trying to be condescending here, just educating, so I hope it does not come off that way.
First off, as most have said, everything you buy that comes with any type of earbud or earphones = teh suck.
Secondly, there is no way that an earbud can produce 20hz. At least not audible to you. Your car stereo, and probably your home stereo probably don't even go that low. The general saying is that people can hear 20-20. Thats 20hz to 20,000hz or 20khz.
Realistically, this is a greatly varying number, as is anything that has to do with humans. As people get older, they lose hearing, and most people can probably hear between 30-40ish hz to 15k-16khz. Stuff lower than that, you can "feel." That is why subwoofers are so much bigger than high frequency drivers, they move more air.
Taking that into account, there is really no way an earbud can give you a good "thump" but there are some bigger over the ear cans out there that can. What these headphones usually do is not worry about balancing your music, and they have what they call a "bass boost." They will put a low end heavy Equalization in the headphone, and that is why when you turn it up, it sounds crunchy, because it starts clipping.
This is all just scratching the surface, there are volumes and volumes written on this subject, and it is actually quite interesting. There are quite a few wikipedia articles on human hearing, including
Psychoacoustics, and
The Hypersonic Effect.
So, back on the subject of headphones, yes, the crappy apple earbuds satisfy most people, and those that want more have the choice. If you are looking for a good, mid priced well balanced earbud and are willing to put the money in them, check out the
Shure E-Series sound isolating earphones. I have the E2c's, and they work great for the gym, airplanes, etc. If Apple were to include a set of E2c's with every iPod, they would be $100 more