Are the continual 'upgrades' in digital photo equipment largely consumer or profit motivated?

If you are into digital photography, you probably know that 'upgrades and 'improvements' keep churning out for every aspect of the pursuit (except maybe lighting). Ex. I bought a digital software add-on a couple of days ago, installed it, printed out the 140 page manual and studied it. Next day I got a notice that a free upgrade was available, which was ok, but the 140 page manual that I printed out and studied was obsolete. At least I didn't have to shell out more money but it wasted a day of my life. How do you determine what's really worth upgrading and what is basically a marketing ploy, and when do you have time to do it?