I have a separate directory on my backup drive just for installers, separate from regular backups, and copy them before decompressing (unless I'm forced to use an unfriendly browser like Safari).
This also makes it easy for me to quickly compare the dates and sizes of different installers, related products, and ultimately even PPC vs. UB vs. Intel-only stuff (sometimes Get Info is quite revealing).
I too deleted the installer in frustration, but simply copied it back from my backup drive once this workaround presented itself. It's rare that I need to do this, but I find that the practice of always saving installers to the backup drive also helps me quickly verify a whole bunch of related products at once, that aren't "managed" like NI products are in their update mechanism. And even those get copied, as a sanity check against their sometimes-broken updater.
