I thought everything worked great as well when I wired up my Xbox to the 27" standard-res RGB I have. Perfect picture......until certain things came up on the screen and my image ripped all to crap momentarily.
As the SCART pinout has no separate connection for pure sync, one has to use the composite video/SYNC/luminance pin to derive the sync signal from. How well a direct connection to this pin works will depend greatly on the monitor you connect it to. Some monitors may have filtering to see only the sync signal, while others, like mine, will interpret certain voltage changes in the video signal as a sync pulse.
Here's a pinout for reference. Note the "combo" pin for sync.
http://www.diyha.co.uk/electronics/scart.htmlAs I said, there is a simple circuit to do the signal stripping. It's my guess that SCART RGB capable TVs have this as part of their input circuitry. As for your monitor working with a direct connection, I have no clue other than that you were luckier than I was

RandyT