Accessible to Everyone vs. Accessible to Every Computer

I have recently been evaluating a couple of different pieces of online meeting/collaboration software. At this point we are looking at 2 different options- iVocalize because of its low cost and simple (accessible) interface and HorizonLive which has more features and is cross-platform. iVocalize is currently PC-only. There are other factors involved, but those seems to be the major issues. (If anyone is aware of any other cross-platform or fully accessible solutions, please let me know!)

While I think either would work for our needs- it presents an interesting dilemna, do we exclude Mac and Linux users or some users with disabilities? (HorizonLive has many accessible components, but the number of features on the software and the way they are implemented would likely be daunting for users with visual or intellectual disabilties). True, many users with disabilities would be able to access HorizonLive with litte or no problem, but Mac users could also use iVocalize with VirtualPC or by using another computer. Another confounding variable is that both pieces of software will be improving in the coming months and undoubtedly other viable options will come into the picture.

Anyone want to shed some light on the topic (or confound things a little more). Please comment if you have any thoughts, thanks.