There are numerous examples of businesses that give away services based either on advertising revenue (search engines) or as a means of attracting customers to their "premium" services or products (Google "Sketchup" as one prime example).
What is distressing about this move by trails.com is that topozone.com had a "give away limited services, charge for premium services" model that was very attractive but trails.com charges the same for either the basic (find a location on a topo map, view one screenful at at a time) or premium (specify an area and produce a custom printable map) services.
That said, they will almost certainly get my $50. The ability to search and find locations and know what quads I need to buy if I want the full maps are really necessities both for my Scouting, highpointing and other outdoor pursuits. Trouble is, I'm still annoyed that I can't grab a screen dump at a time and cut/paste my own maps for free. We already paid for the source data (i.e. the USGS topo maps that our tax dollars fund), so we are paying $50/year primarily for a search engine and enough graphical intelligence to electronically tape corners/edges of adjoining quads when the location is closer to the edge of the quad than the width of the view. (By the way, can someone please explain to me why darned near every interesting trail or peak seems to be right at the corner where you have to buy four quads to see it? I've never figured out how the probabilities work on that...)(ok, that's an exaggeration but you know what I mean...)
I don't disagree with the trails.com business model, but the predatory acquisition of topozone.com and elimination of all free services seems like a bad business decision if it drives customers away because of the entry-level costs. The market will tell...