When I watched the examples of machinima, I was struck by the relative simplicity of the production values. Rather than render scenes frame by frame as some animation does, artists/directors/whoever can rely on the renderings from the chosen game. In some of the examples of Machinima, in particular Diary of a Camper and Red vs. Blue, the works appeared to mostly be voiceover and sound effects laid over gameplay. (Reportedly, early episodes of Red vs. Blue cost $600 for the XBoxes and one day of work per 10-minute episode). Although there are examples with more complexity from RECKONING and off the syllabus, overall the medium does seem to lower barriers to entry.
Accessibility of creating art is a broader topic than I wish to address here. However, the accessibility of creating something like Red vs. Blue strikes to me in particular as connecting to the social nature of games. When one chooses to create machinima, there is the limitation of having the narrative baggage from the game (in addition to the technical ones). Red vs. Blue in later seasons gets very far away plotwise from its initial Blood Gulch Halo influences. This weakness becomes an asset when one wants to engage with the engine as a subject. Diary of a Camper is explicitly about the phenomenon of camping in FPS's (both criticizing it and noting that it is something John Romero, the director of the game, allows for).
Of course, this alone is not necessarily a significant jump over any other cross-media or multi-media work. What is really more significant is the relationship between the creators and the larger, existing community of gamers. By tapping into the game engine, machinima creators not only have a relatively easy way to create art, they also have a broader means of exhibiting to this community. People play Quake and are generally annoyed by campers. I heard of Red vs. Blue in social circles who generally played a fair amount of video games. There seems to be more of a possibility for people to jump from video games to machinima as a separate medium, which is especially important in the case of more experimental work like RECKONING. I'd say a gamer is much more likely to check this out upon a recommendation than they are to check out some random experimental film.
Of course, there are limitations. Obviously, access to cross-platform appeal does not guarantee distribution. I doubt that every mainstream gamer will be convinced to delve into watching clouds from 1-1. Red vs. Blue is not exactly the pinnacle of narrative complexity, especially in beginning.
Moreover, resistance remains in the other direction. Though this is certainly changing, video games in the broader consciousness still lack the prestige of other mediums, which machinima partially inherits. (I showed my friend Queers in Love the other day, and though she liked it, she refused to really even entertain the possibility that it is a game). Technical limitations for machinima exacerbate this, with control and graphics being necessarily years behind standard computer animation in turns of what can be done. In the end, however, I believe that machinima has a positive effect on the ease of making and distributing art.