I'm with @JLeuze - I think he probably showed the tattoo artist the correct version of the logo (mostly based on the amount of space above the W, which really is the biggest different). The rest of the discrepancies probably come just from innacuracies in the process of transferring it to skin. Not sure if a better artist would have done much better of a job but its clearly not important that it be EXACTLY like the official WP logo, the differences are arbitrary.

Actually looking at the rest of the tattoo I can't help thinking maybe he could have found a better artist. He could still do it really, find a serious pro and get the whole thing retouched (or wait till it fades a little and retouch it then to extend its life)