Your C partition is already marked "active". So that's where Win7's boot manager went. It also holds your Win7 system as well.
If you were to install additional OS's, the boot manager menu in this C partition would simply be updated to reflect the current Win7 as well as the additional OS in some other partition. But this C partition would still remain the "active" partition booted to by the BIOS, where the boot process then begins using the boot manager programs which have been placed there by the Win7 installer.
You don't need a "system reserved" partition to hold the boot manager and boot menu if you don't want to or if your install of Win7 was to what already was the "active" partition so that the installer doesn't need to create its own small "system reserved" partition for this purpose. As was explained, this normally only occurs when you install Win7 to a completely empty drive, i.e. one which does not already contain an existing "active" partition".
Since your current operational setup doesn't have a "system reserved" partition, and yet your C partition is also marked "active" and obviously holds Win7 as well, you must have had an earlier OS in the same space (say WinXP? Win98?) which had already marked the partition as "active" when its original install had been done.
Did you "upgrade" from WinXP to Win7? That's one way to have ended up with what you currently have, and it's also perfectly fine.
Or, you could pre-create an empty partition, mark it "active", and then install Win7 into it. Again, you'd end up with no "system reserved". Again, also perfectly fine.