I have noticed you optimized your Programms for USB-Sticks. (Size of Programms/only a single exe file), but I am a software developer, too and in my opinion you can increase the compression of the exe file with Upx. As you can see in the attachment pic, I made the exe more smaller. (from 800 to 300kB). I think this will be good idea for your downloadserver, the downloadtime and the using with Usb-sticks. Here the link to upx on wikipedia: http://de.wikipedia.org/wiki/UPX Maybe you use my idea...
Since UPX is easy to use on a per user basis that's how I'd suggest using it, because every now and then there's always some antivirus software that falsely detects UPX'd files as being infected.
The execution time will decrease, however, the decompression speed is only noticeable on files 100mb or more, and still, it's minor even then. The decompression time is also dependant on the compression level you used, a compression level of 1 would take significantly shorter times to execute where as a level of 6 may take longer. There are also several other options you can configure using the command-line that may or may not affect the performance.
UPX is great - but it should remain a user preference, if they know about UPX and wish to use it, they may, but as CCleaner wants to maintain their credability for supplying a great prorgam, they don't want UPX to endanger their respect.
PS - Thanks for spreading the word about UPX, I have never heard about it before now
Wait...you just learned about it, and you are coming off as a pro???
Online documentation!
I would personally avoid using UPX for downloadable software due to the fact that antivirus every now and then gives false positive detection of UPX compressed files.
With modern compression such as RAR and 7z (excluding ZIP) most notably LZMA compression in installation compilers such as Inno Setup -- UPX is no longer needed to "save file size."