Because the read/write head is so excruciatingly close to the platters, the slightest blemish on those blazingly fast-spinning disks becomes a huge speed bump, which destroys data, and eventually the entire hard drive.
XP use to require manual check disk, but folks didn't know how/why to do it, so they ignored this near critical maintenance task.
MS probably figured to make it automatic run every so often to alleviate stress in their audience about HDD crashes...not sure on that though.
I use SpinRite for all partitions so I don't worry with multi-platform system checks, and Windows 'check disk'.
Please don't WUBI. If you're gonna do Linux, commit.