are these the ripped files of ISO that's why they are smaller size?
No, they are compressed ISOs.
They can be ripped, or they may not be.
yeah they are compressed with programs such as YACC (yet another cso compressor) and such. . . they can sometimes save you ALOT of space in your ms.
You also can use UMDGen to compress or un-compress it (ISO or CSO).
Thanks for the info Whit3f0X, but please do not bump extremely old threads - thanks!