I am a bit confused about how Microsoft Office Powerpoint 2003 manages the size of the PPT. You can try this out. Follow these steps:
>> ... Create a fresh new PPT. Don't write anything into it.
>> ... Just save it on to your disk.
>> ... Check the size of the PPT file. For my case it is 8 KB.
>> ... Now save the file again (Ctrl+S). And now check the file size. It has changed. I got it as 13 KB.
>> ... Now keep saving this file again and again without writing anything into it (No change). You'll find the file size changing with every save you do. For me, it kept on increasing by 1 KB with every save.

Discovery: No change to the file, nor to its contents (absolutely untouched). Why is its size increasing with every save? Any answers?

Note: I tried doing the same with Powerpoint 2007. Everything is fine there. The size of the new PPTX file is 29.3 KB and the file size is not changing with subsequent saves. Looks like Microsoft has fixed the bug in this release.