I'm not sure who, at DeLorme, is responsible for deciding whether or not to put money into developing for OSes other than Windows, but I'd like to put in a few words...
I am very interested in finding a good GPSr/mapping solution and I've been an Apple user since the early 90's. I own Route 66 and it is by far the best mapping software available for Mac OS X that I am aware of for the simple reason that—although it isn't particularly good—it is the only thing available (as far as I know) for Mac users.
I have seen many people say something along the lines that "Apple is a minority of computer market share, comprising less than 10% of the market." I will not debate this as it is very certainly true. However, I would like to point out that as far as selling a software product goes, looking at overall computer "market share" might be rather misguided. It might be more prudent to identify who your target audience is and see if it is large enough in a given sector. While "most" people who buy a computer will buy a computer that runs Windows, how many of those people are actually interested in a GPSr/mapping solution? I don't know the answer to that question, but I do know a few things about people I personally know who own Macs: most of them are 20-35yrs old (okay, so that's mostly to do with how old I am), all of them own cell phones, most of them enjoy outdoor activities and traveling. I realize that this is anecdotal—I don't have the resources and don't really care to bother conducting a survey—but I suspect that there may be a more sizeable demographic amongst Mac owners of the kind of person DeLorme wants to sell products to (if DeLorme was interested in producing Mac compatible products). I realize that "less than 10% of computer market share" sounds small, but this is still about 5 million NEW Mac owners every year and growing... perhaps Apple's market share of technology purchasing consumers seems small to some people, but I'm pretty sure Apple's stockholders aren't toooo unhappy.
A while back I would have been able to say that the market for GPSr/mapping in the Mac community is completely ripe for the picking, since there has been little in the way of commercial support. However, it seems worth noting that Garmin now fully supports Mac users who own their GPSr units. Still, from what I have read, the features of the DeLorme mapping software are quite good. I would really love to be able to justify buying a PN-40 with Topo 9, but as things stand I would never be able to access most of the features that I find appealing.
I am interested in a GPSr/mapping solution primarily for navigating when I go dualsport motorcycle riding, although planning road trips might be easier if I had Street Atlas on my laptop as well. Hiking, camping, mountain biking, and perhaps geocaching are also among my interests. Nevertheless, Garmin seems like the logical choice since I'll actually be able to use it, and also since it is almost the defacto name for GPSr... (my mom can't even get the letters in GPS in the right order, but she knows what you're talking about if you say "Garmin")
Anyway, for what it's worth, there are my 2cents.