[MacSail]

Be a bit more specific, which brand/model GPS receiver(s) are you referring to?

Sure - the list of devices I've tried follows:
Magellan eXplorist (forgot the model number)
Garmin Oregon 200
Garmin Colorado 400c
Magellan Triton 500
Magellan Triton 2000
Garmin USB receiver (forgot the model number)
Bushnell ONIX 200

In fact, only the BU-353 works without an adapter and I've gone thru three in 2 years - not something I'd trust. Yet, except for the ONIX all of the above receiver and handhelds work with my other Mac based GPS programs -- without any adapter, using the included USB cable.... except GPSNavX.

My issues lay with the inability of GPSNavX to work with handheld devices, and less so, the inability to work with the hundreds of other receiver pucks available at everywhere from marine stores to Wal-Mart. When I experience a component problem while sailing I'm not comfortable with having to special order and rush ship a single particular part that can delay my departure and float plan by a week.
The BU-353 may be cheap and only a tad slow compared to modern equivalents, it really does suck power from your Mac and if you factor in rush shipping it's over $100.

With respect to your assertation:

Other than Garmin's USB cable (which does not support NMEA-0183 data - the standard for marine instrumentation), my experience has been USB GPS receivers, USB AIS transponders/receivers and USB Multiplexers work great with MacENC and GPSNavX.

I refer to and quote directly from my Garmin Manual (page 34): Interface Output: USB NMEA 0183

Not sure how you can get a Windows PC for less then the price of GPSNavX and a cheap USB GPS such as the USGlobalSat BU-353. Please post details.

I'll just have to refer you to any number of MicroSoft commercials. Mac's aren't cheap. Here's just one I thought would be a nice fit:
A waterproof CF-52 P8400 2.26GHz Toughbook with Centrino2 vPRO and built-in GPS: $1559
I'm not here to pimp any PC software alternatives, but there are more than a few that I'm sure we all know of.