Bruce - There really isn't a 10 hour battery.
What they are talking about is the newer battery has a few more Milli Amp hours in storage. While it will buy you a few minutes more, it won't really lengthen the amount of run time by that much when you put it into the older systems.
You see its more than the battery, it's the about of load the system has. The newer model which intro'ed this newer battery boosted it had a 10 hour run time which is were that came in.
The newer CPU and support chips the newer system had lowered the battery load which is what lengthened the system run time.
Putting the battery into an older system won't really offer the same amount run time. We measured about 10 minutes more in a 2009 MacBook Pro doing very little.