Charge on an electron is rounded
Ask Wolfram Alpha what is the charge on an electron and you will get an answer of 1.6021765x10^-19 C.
But the best avaiable data is the CODATA 2006, which is what is reffered to by both NIST in the USA and NPL in the UK.
Wolfram Alpha have the value from CODATA 2006, but it has been rounded to 8 significant digits. The internationally agreed value is 1.602176487x10-19 C, not the value Wolfram Alpha gives.
So far from being a 'primary source' as Wolfram Research claim, it is taking primary data and rounding it. Wikipedia has the right value.
I'm a user of Mathematica and find that program impressive, although the free open-source Sage looks as though it will be a thorne in the side of Wolfram Reserach. I was impressed the day I first see Mathematica - more than 20 years ago. But I can't see much of use in Wolfram Alpha. It appears to be a poor man's Mathematica. For most things web relatved, google is far more useful.
I'm sure Wolfram Alpha will improve over time, but I can't ever see it being too succesful myself.