Yes, you can use it, in lesser quantities.
About the second question: the reason why we have not 33-34-33:
These number are the percent of weight of N,P, and K.
For example, N is a gas, so we need some molecules which includes N (it is impossible to have a solid 100, 0, 0 fertilizer) . Such molecules could include C, H, O, S, (and maybe other atoms). So they take some of the remaining weight to make 100%.
10-10-10 is probably not a dilute version of 13-13-13, but other molecules. If you are going professional, the molecules matter (and not just the numbers): some molecules decay very slowly (so it is cheap to do a heavy fertilization, but just every few years), some are very quick (so for emergency fertilization), some could acidify too much the soil (and they could have negative effect to other fertilizers), etc.
If you read carefully, the fertilizer should tell you which kind of molecules it contain. I confess that I never checked that the sum of all atoms in fertilizers (as advertised) will be really 100.