I'm sorry, but do you waste time entertaining any conspiracy theorist who comes a-knocking? I didn't think so.
First, exhibition matches count for nothing. Read the comments after the matches (and watch them) and you'll see that they are hardly serious. At the very least, they say nothing about what would occur in an official match. Not to mention that Sampras only beat Federer in one exhibition match, so "a couple of times" is pushing it.
The courts have been slowed down, but to suggest that it was done to hinder Roddick and Blake is a joke. Watch some of the matches between those two and Federer on some of the faster surfaces, they generally weren't very pretty. Any advantage Roddick would gain on serve would be negated by the advantage Federer would gain on his own serve. Federer would often out ace Roddick, no matter the surface.
Slowing down the courts was likely a response to the style of tennis that was being played on some courts in the 90s. Many people weren't fond of some of the brainless points that were being played, so they did something about it. There is nothing sinister about it.
The rest of your post can hardly be attributed to any kind of intellectual thought, so spare me the lecture.
Creating phony public backlashes? Show some proof before you make such a claim. Random internet websites aren't going to cut it.
The fact that the pros use "low powered" racquets doesn't mean they can't crush the ball, only that they must take a full swing in order to generate a lot of power, unlike the cheaper twenty dollar racquets which are designed to give low skilled players the ability to take slow swings and still push the ball where it is needed.
Nobody is saying you can't put spin on the ball with nearly any type of string, only that the current string setups are better at generating spin. There are many discussions about this (even on this forum) so save me and everyone else some time and do a search for yourself on why this is happening.
What is your source for putting metal in the balls? I have a few tennis balls that were used in somewhat recent professional matches. If it comes down to it, I have access to equipment (access to people who can do work like this in other departments) that could be used to determine the composition of one of these balls. It doesn't take a physicist to make balls heavier without resorting to some type of metal weighting system.