I think it's like Hollowdweller says, the conventional definition of a bushcraft blade is what Mors Kochanski and Ray Mears pushed. If you look at Mors' definition in his Bushcraft book, it's nothing more than a full, exposed tang puukko. Which, incidentally, is what the current crop of "must have" bushcrafters are, like the Skookum, Koster, BRKT Nebula, etc.
Nothing wrong with that.
Lately, I've broadened my definition. Pitdog is largely responsible for this in proving that his Tracker (a design I really don't care for) works for him. Running with the "any knife that can do woods tasks can be a "bushcrafter", I took my Busse Hellrazor -- a purpose-built fighter if there ever was one -- and did all kinds of "crafty" stuff. Guess what? It kicks ass in the woods.
So, my definition is now more in line with the other guy's: whatever knife you can make work for you in the woods, is your bushcraft blade.
Note that what works for me may not work for you, and vice versa.