Didn't think of it the other day, but sig did, go to http://www.everymac.com and then any of the Apple products listed and then any particular vintage to get all of the details available.
What Apple does iS no different than anyone else in the computer industry, constantly upgrade equipment. As the end user you have to just make a decision and buy what suits your needs. A user who gets caught in the trap of waiting because something better is just around the corner will never get a new system.
I boughtt my current MacBook Pro and a month later the standard i7 was raised another 0.2 GHz. Such is life. But I use that machine so heavily I could not really have waited.
just some thoughts.