Yeah, that's been my one minor complaint. It's clearly a plot device, and one that doesn't make much sense. The only thing I could think of is that it was something more generic in Worf's cells that was useful, but that's a stretch. This ep also established that the Romulans are biologically distinct from Vulcans, even though they share many genetic traits. They are separate species, and the Vulcan techniques Crusher tried didn't work.