On some other airlines (i.e. United), while tracking the status of a flight later today, or even tomorrow, you can see the earlier legs on the same aircraft and track the inbound flight. This is a very useful tool, because it can help you anticipate delays hours before the airline officially declares them.

I've noticed that this feature is less frequently available for JetBlue flights, and with much less lead time (either on jetblue.com, or on a site like flightaware.com that aggregates flight data from every airline).

I was wondering if this has to do with a difference in operations (perhaps JetBlue reassigns aircraft more often) or simply a difference in publicly available information. For JetBlue, is there a site that tends to provide this info more often or earlier than other sites?

These features can be fun, but are relatively useless in the context of the legacies such as UA, flying into hubs. The aircraft currently scheduled to make up your flight can be substituted at a moment's notice, so I have stopped worrying about the status of the inbound unless it is an outstation where it is self-evident that the only inbound aircraft is the only game in town.

Good point. And, like you said, at a small outstation you can often easily figure out the inbound flight.

I wonder what's behind the decision of some airlines to provide this data (especially if it's frequently inaccurate) and others not.

I've noticed that our tails swap out quite a bit through out the day. I usually work red eye turns out of Boston and I will often check on what tail we are taking out west, usually to see where it is coming from but more to see if we will have flyfi for the evening. More often than not the tail will change a couple of times through out the day.

So many of the B6 routes are "out and back" from a hub that it is easy to find the plane for half the flights. For the other half the tail swaps happen so often that it is probably better it is not published.