When you say "recovery disk" I assume you mean a recovery area on the hard disk as opposed to a recovery CD or DVD.
On a hard disk this is a often a hidden partition, which will not be seen by the user.
You say 12Gb of programs but a recovery image is only windows and a few utilities so it is not going to be 12Gb.
And yes, it is compressed, not a Zip file, but similar concept.
I have an Acronis backup of my complete XP disk (with Microsoft Office and a whole load of other programs) and it come to just over 5Gb - Vista will be bigger.
It is not likely this recovery image on hard disk will get corrupted itself, it is usually one large "file" so the chance of it getting corrupted is low.
And yes, if there is a disk failure you could lose this recovery partition, which is why it is always a good idea to make a recovery DVD if you computer gives you that option.
Have a look in your PC documentation to see if there is a program you can run to make your own recovery DVDs.