A quick summary for those not familiar with Macs and/or iPhones:
On the Mac, there are two applications: iTunes and iPhoto. In addition to being Apple's portal for all their online shops, iTunes is responsible for sync'ing things between the iPhone and the Mac. iPhoto is the photo library application, storing all the photos from any cameras connected to the Mac, organising them into dated events, albums, etc. When you connect a camera that has some recorded video, that also gets sucked in by iTunes and stored in iPhoto.
Over on the iPhone, there are two other applications: Photos and iPod. Photos is used to view all the photos on the phone, either those taken by the local camera, or those sync'd across from the Mac by iTunes. iPod is used to listen to music, play videos, etc., working off things either sync'd across by iTunes, or downloaded directly on the phone.
Normally, when you sync, iTunes sucks video from the phone into iPhoto, but it doesn't send them back in the other direction. There's a setting, "Include videos", that changes this, and it tells iTunes to send a shedload more content back across to the phone.
I don't know whether it's just a plain ol' bug in iOS 4.3, but on the iPhone 4, Photos doesn't show videos, only photos, and iPod's "Videos" tab only shows those videos that have first been imported into iTunes and then sync'd. Neither application seems to want to show all the videos that have been copied across.
I'm wondering whether it's that each app's development team thought the others were doing it.
Maybe one of the apps used to; I don't know - I never tried before upgrading to iOS 4.3, but Googling this problem suggests that the "Include videos" setting has been there for quite a while, so you'd think someone at Apple would have tried this.