One of the factors I've heard mention is the cost and availability of globes for data projectors.

Then on top of what irneb has said, the other fact is the colour range. If you are looking for movie quality, you need high colour range and resolution. If it is mainly text, graphs, still pictures this is less critical.

Finally, there is the issue of size which comes down to just how portable you want your data projector to be. This can be a real issue if you are going to be flying - I wouldn't be excited about running a data projector through checked luggage. As with many things nowadays, smaller can cost a fair pile more when comparing two machines of roughly equal features.

I hear you on how confusing the range is. It just feels like an endless list of trade-offs.