I kind of took it that having an EZ-Pass is basically a fact of life in the north east these days. So what happened though say you are on the PA Turnpike and you need to get off the thing but you don't have an EZ-Pass for an EZ-Pass only exit because you are just passing through with cash only? I've always wondered about the same thing with the Sun Pass only exits on the Turnpike here in Florida. I saw it in Maryland it was a $25 dollar violation, so I'm just assuming that you are SOL when it comes to those EZ-Pass only booths? 
You might be surprised at how many people don't have E-ZPass. There are a variety of reasons they cite. I assume many of the large number of New York City residents who don't own cars don't have it for obvious reasons. Some people feel they don't use toll roads enough to justify E-ZPass. Some people don't have a credit card, don't want to use manual replenishment, or aren't willing to give their credit card number to a tolling authority. Some people view it as giving the toll authority (or whomever) an interest-free loan due to the need to put a certain amount of money on the account up front. Then you have some people who simply don't understand how it works and are reluctant to get it (my father, who is not a technical buffoon, didn't understand it at first).
Then you have the conspiracy theorists, people who are convinced E-ZPass and similar programs are Big Brother in action. They figure it'll be used to track your movements or to give you a speeding ticket (there are all sorts of false stories about the latter on the Internet). I know one guy who opposes the WMATA Silver Line project (Metrorail to Dulles Airport and beyond) who for some bizarre reason thinks getting an E-ZPass is supporting Dulles Rail (even if he never uses it on the Dulles Toll Road).
The argument about not using toll roads very often may have some validity depending on where in the E-ZPass region you live. I can understand it if you live in the DC area and seldom travel north, for example. If you don't use E-ZPass facilities very often, I guess the idea that it's not worth it to you to get one kind of ties in with the idea of giving them an interest-free loan because you're tying up $35 (or whatever the issuing agency requires as the minimum balance) on the device.
Regarding the E-ZPass Only interchanges in Pennsylvania, I haven't used any of them, but one thing to understand if you aren't a regular user of E-ZPass facilities is that some E-ZPass member agencies persist in using gate arms on E-ZPass Only lanes, usually because they converted the old "Toll Machine" lanes (also called "Exact Change" in many states, i.e., you pull up, there's an arm blocking the way, you throw coins in the basket, and the arm goes up) but didn't remove the arms due to concerns over toll cheats. The New York City area is notable in this respect. If you enter an E-ZPass Only lane that has an arm, you get stuck. If Pennsylvania has that setup on those special exits, that'd be a very good reason not to use them without E-ZPass.
Interesting thing is, "jeffandnicole" mentions (rightly) how there are plenty of signs saying what is or is not an E-ZPass lane, but some people still manage to get confused, perhaps because they're not local and they don't know what E-ZPass is. Seems simple enough to me—if you don't know what it means, don't go into that lane—but apparently some people don't think that way (maybe because they're focused on the shorter line there?). In fairness to those people, in some places the signs can be a bit overwhelming. Virginia, for example, puts an E-ZPass sign over every damn lane at the toll plaza because it can be used in any lane, and Virginia also doesn't use the flashing yellow light to denote the E-ZPass Only lane. It means there are a heck of a lot of E-ZPass signs in an area that already, by its nature, has a lot of signs. New Jersey, on the other hand, posts a green sign prior to the toll plaza saying "E-ZPass Accepted All Lanes" (it used to say "E-ZPass Signed Lanes Only" when you had to use specific ones) and another sign saying the flashing yellow light denotes an E-ZPass Only lane. True, some drivers may miss the green signs, but it reduces the visual clutter at the toll plaza.
Florida's "toll-by-plate" system of charging a single fee at the end of the month aggregated across all trips is a lot more forgiving to the motorist than the system here in Virginia on the high-occupancy/toll lanes or in Maryland on the all-electronic Intercounty Connector. On both of those facilities, there is a per-TRIP charge. In Virginia, it's in the nature of a penalty ($12.50 per trip if you wait to pay until they bill you instead of paying online!) for failing to comply with the requirement that you use E-ZPass; in Maryland, they state the charge is intended to help defray the cost of using your license plate number to track you down to send you a bill.
