We just don't know the reasons why the Iranians seized the crew. I am sure the UK is learning why through their diplomatic contacts with the Iranians. Once we know their demands, we can decide on how we want to proceed.
It's true that we don't know. It's also true that it's different now than it was in 2004. And we know more about what specific activities the Iranians are involved in within Iraq's borders.
It's helpful to watch what's going on in Iran internally. Because it's reasonable that the true intentions or wants of the Iranians may not be stated in these negotiations.
Ahmadinejad has stated openly that he doesn't respect the West and he belittled the "processes" of diplomacy. This doesn't mean that he doesn't know how to use the tools of the West against us. There may be a specific request in these negotiations with an intent to divert attention from the underlying issue.
He's not in good shape at home or in Iraq and these are important notes to keep in mind.