AS said, he can't be that scared of needles if he gets tattoo's and has had blood taken for previous fights, infact he's had no problem as long as the blood tests weren't for drug testing which is incredibly suspicous to be honest.
Asking for blood testing is not suspicious, you think the other guy might be cheating, you ask for the testing, your entire reputation is resting on the very biggest fight of your career, you're going to retire after this fight as the single greatest pound for pound fighter ever, or 2nd, its a BIG difference, you wouldn't want the other guy tested properly, I certainly would.
As has seemingly been said, theres been a very big comprimise by Mayweather, and Pacman still refused.
As for effecting training, being scared of a needle(which doesn't seem true anyway) wouldn't effect your training, nor would taking one small vial of blood. we're not talking about a pint of blood for donation that after you might be dizzy from, you're talking about a ridiculously small amount.
Now unless you think Mayweathers been training his body to recoup a tiny amount of blood faster than his opponent(how do you train bonemarrow?) then whatever miniscule and stupid effect it might possibly have, would be an equal disadvantage to both fighters.
Theres two things here, its pure PR to introduce more "hate" between the fighters, one huge part of the income from a fight night like this is box office, the other is how much the betting world makes, Vegas and other places rake in millions and millions on bets for big fights. The thing is, the more one personality irritates you, the more likely you are to want to pay to watch him being beaten, or put a bet down on the other guy whipping his ass.
The other possibility is Pacman really does have an issue with blood being taken at a certain stage, and you have to question the reason...... its not fear of needles.
Unfortunately blood doping, cheating, performance enhancing drugs can be hidden, people are spending millions a year on research for new drugs and new ways to hide them.
Too many past champions in all kinds of sports end up being known as cheats but way after the fact, sprinters, boxers, American footballers, baseball players, basketball players I think have been found out/admitted it years after they quit.
As someone else said, Margarito cheated in a ridiculous obvious way right under everyones noses, potentially for years without being caught, purely because no one actually looked for it. Lots of boxers could have been cheating easily for years because no ones actually testing blood, would anyone possibly question it if Mayweather was now asking for gloves/wrapping to be triple checked before the fight, no, because there's a precedent. So would it be fine for Mayweather to ask for blood testing if someone came out in the past year, ex boxer saying he was cheating the whole time but no one tested his blood? No, everyone would say its fine and it would probably become standard.
Mayweather really isn't asking for much at all, and Pacman is looking increasingly suspicious.