You asked the question in the right place, but since you seem to be uploading binaries into your PPA rather than source code, the chances that you will get a size increase is small. PPAs are meant to have open-source software, where the sources are uploaded, and binaries are built on Launchpad's servers. If you want to use this software on your own computer, you don't need a PPA for this.
I know for a fact that Android Studio is open-source, and gem5 is also open-source (although it has some closed-source parts), so one of your reasons is invalid.
Another reason source packages are built for each Ubuntu release is because there are different libraries and library version in each release, and so a binary that works on one release may or may not work on another release. Source packages are also built for each architecture because while an i386 application can technically run on amd64, it requires the use of i386 libraries, whereas an amd64 application only requires amd64 libraries (amd64 applications cannot be run on i386). In addition, different architectures have different "defaults" (an
int may be 2 bytes instead of 4 bytes), and each application has to be built on each architecture to account for that.