I am not familiar with any airlines that charge for carry-ons, but for example I know that many hotels in downtown Las Vegas have mandatory "resort fees" that on many nights actually exceed the nightly rate shown in booking engine search results - so the actual cost of staying is more than double the advertised rate. Most booking sites have heard so many complaints about this that they do show the total (including resort fees) just prior to booking. But the "headline rate" - the one shown in search results and used by the sites in arranging results by price - is the one sans resort fees.
Taken to an extreme level, hotels could advertise a $1 nightly rate and a $200/nt "resort fee". It wouldn't surprise me if this actually started happening, given the competition among hotels to show up first in search results. It sounds like some budget airlines are headed in a similar direction.