The fact is, the Iranians have some British troops, and the U.S. recently took several Iranian diplomats in Iraq into custody, accusing them of helping the insurgents.
For this reason, this incident doesn't seem like a coincidence. The most likely intent by the Iranians is to hold a prisoner swap. This means, thankfully, that the British who were captured are probably being treated quite decently. The hardware they had -- inflatable boats -- was nothing to write home about, so there's no major risk of Western technology or intel falling into Iranian hands.
The Iranians should want a prisoner swap. The British -- and a weakened Blair government -- should want a prisoner swap. The U.S., however, might want to drag the British -- kicking and screaming -- into a major political conflagration, in order to beat the drums for tighter sanctions against Iran, if not actual military steps against Iran.
They'd basically say words to the effect that we don't negotiate with terrorists / under duress / don't release criminals, etc. (Of course, we do, but that's beside the point.) This situation is quite different than dealing with Taliban headcutters, and we shouldn't forget that fact. It's more akin to dealing with the Soviet Union, and, during the Cold War, prisoner swaps like this happened ALL THE TIME. We should be glad they did, as they helped to reduce the chances of direct confrontation.
The Iranians might not have nukes yet, but those who think that we should be fighting them in the middle of two other major confrontations, are irrational, corrupt sociopaths. Unfortunately, many of the leading neocons fall into this category.
Presumably, if the Bush administration wanted to cause a larger incident, they would try getting the Iraqis to not approve of a prisoner swap... but would they? Depends how whipped they are, I guess. Blair's government could probably persuade the Iraqis to release any Iranian prisoners they might have, assuming that the Iraqis are the ones holding the Iranians... but Blair is enough of a toady to quite possibly follow Bush's lead, no matter how self-destructive such a policy would be.
Meanwhile, expect this event to have a negative effect on oil prices, on consumers, and on the stock market. Billions will be lost. The best thing for all concerned is some soft words from all corners, and for a quick, quiet diplomatic settlement to this issue.
Maybe this time, the Republicans can find a way to release the hostages without giving the Iranians weapons, too...