Softimage is the highest caliber program and it is used - almost without exception - for the majority of final renders in film. This is because it has exclusive license to the the fastest, highest quality renderer in the business - MentalRay. This renderer is considered by academic circles to be superior to Renderman on many fronts: speed, quality, flexibility, and features. Other programs are often used for modeling or animation, but that's the nature of the business - if a tool works, you'll find it in use.
The reason they are giving away demo CD's is that they're releasing XSI version 2 soon, which FAR surpasses the version 1.5, which they're giving out as "an accelerated training and demo CD" (with the following limitations: some features are disabled, all images are watermarked, and you can't save the scenes) They're hoping to get people used to the interface, so that when 2.0 comes out, people will feel comfortable using software that will cost them some $13,000
Lightwave does not dominate the film, television, and effects market, at least not as Arioch suggests. That title remains in the the hands of Softimage and Alias|Wavefront. Compared to 3D Studio Max's Hollywood market penetration, Lightwave does indeed "dominate" that market, as 3D Studio Max "dominates the gaming market. Lightwave 7 actually includes a Non-Linear-Animation system, though I doubt it's quite as effective as XSI 2's.
For comparison's sake - quality/features - Softimage is to Alias|Wavefront is to Maya (made byAlias|Wavefront) as Lightwave is to 3D Studio Max is to Blender.