Again you're missing the point which is not how good the newer versions of the Windows defragger are or aren't. The point is that because earlier versions were so bad, many people will automatically look for a different solution and never even try the built in one. That's the answer to why people look elsewhere. They assume, rightly or wrongly, that the built in utility is inferior and never use it.
As far as automatic defragging goes, I never have it turned on because I think it causes needless wear and tear on your hard drive. The automatic feature of the built in Windows program does not do a full defrag but rather only optimizes system files and performance of those when it kicks in. In Win 7 it only runs for a short time if at all. I play a lot of PC games and every time one gets a major update it causes massive fragmentation of the game files. These files can be a few gigabytes in size each so the fragmentation percentage of the drive as a whole goes up drastically even though it's only a relatively small group of files that are actually fragmented.. Keeping those files contiguous produces significant improvement in game performance. Other than after game updates or installations, I rarely defragment at all.
One of the biggest reasons why I don't use the Win 7 program is that it gives you absolutely no information as to what it's doing when it runs. I turned it on one time and that was it for me. I didn't even let it finish. I at least want to see a graphical depiction of the file placements on my disc and the Win 7 utility doesn't have that where even the inferior XP utility did.
Here are only some of the things the Win 7 program can not do that Puran can:
It can not consolidate free space and fill gaps in between files to prevent future fragmentation. (very important)
It can not defragment the MFT or other metadata.
It can not be used to defragment only specified files or folders.
It can not be set to exclude specified files or folders.
It can not be set to run at boot time.
The Win 7 utility is still a basic tool in comparison to other alternatives. End of story. I'll have to read up on how the Win 8 version has been improved but my motivation is somewhat lacking as I don't ever see myself going to the newer OS.