Welllllll... I repeated the exact same test 3 times, with Camino, Safari and Firefox being set as the default browser. Exact same results with all 3 browsers. Except for the first launch of the browser, Open As Web URL only shifts focus, doesn't "open/load" the file.
Tried another app that sends URLs to the default browser, it worked 100% correctly.
Re-read Wim's post... VERY odd that it appears related to the CPU (I'm running PPC)?