Am I required to install expansion joints at all interior doorways for Pergo?
Pergo want to absolve themselves of as much liability as possible, so they require expansion joints at all room connections. Obviously this isn't always necessary to prevent movement issues. 

You'll have to make a risk judgement. Do you want to absolutely prevent buckling and shifting issues and leave Pergo's warranty intact?  If so, follow Pergo's guide. Or are you willing to accept liability for repairs of any movement issues as a compromise for nicer aesthetics? If so, read on....

I would obey the 40 foot rule. That is, if you're connecting two rooms whose combined width doesn't exceed 40 feet, run the flooring straight through. If it does, install a transition with the required gaps. Connected closets don't really need transitions, for example. This should leave you with far fewer transitions than Pergo calls for, but confidence that you won't have movement issues. 

Should you find that you do have movement issues, you can always cut in new transitions as needed. The mounting channel for Pergo's T moldings can be installed after the fact and the molding set in place.