Electrons and Quarks

[colinha]

Electric force charges on quarks are +2/3 and -1/3 for up and down variants.
The charge on an electron is -1
Quarks balance in groups of 3 to give a net charge of +1 or zero in nuclei in atoms.
The fact the charges on electrons and 3 quark nuclei match allows atoms to exist.
My question is why these apparently unrelated particles balance in this way. Is it posible that the quarks could have had charges of 3/4 or 7/8 or some other value and hence atoms would not have existed or is there some fundamental reason that these charges were inevitable?