Incompatibilities with Acrobat Reader 5

I already wrote that per mail, but I never got an answer, so I try it here.
Some months ago I recognized that all manuals have been updated. They still look the same, they still have approximately the same file size, but now they can't be opened with Acrobat Reader 5 anymore. And now I have two questions:

1. Why? Why was that done? Why updating a complete set of thousands of manuals when the new versions still look the same and the only difference is the fact that an older program cannot open them anymore? Where's the advantage. Dear webmaster: Have you been paid by Adobe to include this incompatibility, so that people download the newest version of the Acrobat Reader? Otherwise I don't see a reason to take the trouble to update everything although the only change will be something that's basically a disadvantage.

2. Are the old versions of the manuals still available somewhere? I'm not going to install Acrobat Reader 6 because it is much too bloated and three times bigger than version 5. So, I need to know where I can find the manuals that were online before everything was updated. If anybody could help me, that would be great. Thanks.