Why are some people better at math?

Perhaps from learning it manually.

Members of the "greatest generation" (and later) will tell you that these devices they used in school taught you something about the relationships between numbers that a calculator cannot. Slide rules are really quite elegant, and this photo of part of one should by itself allow interested observers to absorb qualities about numbers. It may even provide you with a small window into the fascination some of us have with calculations--or at least the rhythm of arhythmetic [sic]. (Photo courtesy of Derek Ross; please visit his site for more information and a variety of interactive virtual slide rules. If they appear out of alignment, try a different browser.)

While the site has detailed instructions for their use, I recommend getting the satisfaction of figuring them out unaided. If you're not familiar with the concept, you might find that site's metric converter to be a surprisingly fast and intuitive introduction (after following the link, flip the rule over as the top button suggests). Note that the center section of slide rules moves from side to side (as does the cursor window for ease of alignment).