Yes, for the same reason. It's not the drive that's slowing down. (If you are patient and read this through, I put my solution at the end).
Windows systems accumulate "bloat." Installed apps that run some part of themselves on startup. Patches on top of patches on top of patches. Malware. Uninstalled apps that leave bits of themselves behind. This stuff doesn't just eat up disk space; it slows down registry usage and eats CPU cycles and, if you are low on memory, memory.
That's why, as you note, a system is fast after initial install and slows down. Some of it is legitimate; as you install more and more software you tend to have hooks that preload some DLLs or even, Heaven help us, check for updates every time you boot. Some of it is stuff that you think you removed. Then there's the crap that you have on your system if you have ever played a CD from Sony (smirk).
Some people do clean installs every so often. You can even automate the process of re-installing and re-configging the software if you are a real gearhead, but it can be a pain.
One man's solution, and I don't claim that this is optimal. I do a clean install, all updates, install antivirus, do a full sweep, and take a backup. Every time I either install new software or just feel bloated, I :
■Take a backup of my bookmarks. That's all the persistent data that I have on my OS drive.
■Restore the backup to the OS partition. Boom. Wipes out everything I've done since then.
■Run all updates and another virus scan.
■Install the new software, repeat any config changes that I have done since the last OS backup.
■Backup the OS.
As a result, I can restore my OS at any time to a state that has, effectively, been running for less than a month. Ghosts of uninstalled software go away, even infections since the last backup go away. It keeps me happy.
Obviously, all of my data is in a separate partition, and I keep the My Documents folder on another drive entirely. Some games save into Documents and Settings / Username, so you have to configure new stuff carefully to stay out of there, or have a job to backup key directories from that tree (which is my solution).
It's fairly extreme, but it works for me.