Odd behavior backing up

I've just spent 1.45hours on tech support to figure out what the heck is going on and this still doesnt make much sense to me.

I usually do a sector-by-sector backup (when I was using version 9 of the product) and then I was able to restore just fine.

But now I am using WS2008R2 and so I bought version 10 for backup and recovery advanced server.
So, I thought I would just do a "full" backup of the disk (volume, not files) which will be much quicker and file size would be smaller (as its not sector-by-sector).

So, I have 16GB being used by the disk. When doing a full backup including MBR/System Reserved, the TIB is shown to be 6GB! This makes no sense.

So, I explored the image and see some files missing like pagefile.sys and whatever other files. The point is, "Full" states it will backup all the files but clearly, the file size is much much smaller (no compression, no exclusions). Why?

i was assured that when I restore the image, it will work just fine - I will test this but I have my big doubts about this as I dont want to find out down the line that any software I install, may require some files that the backup missed when backing up....

any ideas? is this how it works? Why does it show much less file size than the actual used disk space of the HDD?