As already mentioned, they don’t really need to acquire someone else’s technology, but it might have made sense. The worst thing to come out of Adobe doing it on their own is the proprietary engine that in the first round didn’t let you export models to other format. With CS4, you can export OBJ and others, so that’s a bonus.
I really don’t think Adobe wants to engage in actual modeling so much as position PS as a more important tool in a 3D workflow. A benefit to this is giving 2D artists and photographers easier access to 3D for design or stills compositing. I’m a big advocate of using 3D in PS in not-so-obvious ways.
Given the amazing tools and talent out there in the 3D world, it’s easy to look at PS and wonder why they are bothering. But for those of us just adding 3D to our 2D work, it’s a very nice way to engage and start learning - we have safety nets 
As an example of what I mean, as a photographer, I use the 3D elements to help generate realistic shadows (or even just guides) when blending multiple images - often times, a very simple primitive or two can suffice to give me a ‘good enough’ approximation of lightfall. For that matter, I’ve also used 3D scenes for previsualization before setting up a studio or location shot. This is something I would not have done because I wouldn’t want to go out and buy additional tools - the learning curve is just too great to get a good return on investment here.
Now, could the tools be better? Absolutely. Personally, I would kill for a real UV tool in PS rather than a simple grid overlay. And it certainly could be easier to keep track of materials, meshes, etc. Each of these additions would be great, but it also requires a lot of resources for the engineering team. I really don’t want Adobe to lose focus on PS as a premier 2D imaging tool. So don’t expect CS5 to blow you away with amazing 3D tools if you are already a 3D artist, but do look at the new stuff in context of 2D artists. Adobe isn’t out to replace anybody’s dedicated 3D tools, but instead they want to be a more important part of a team workflow.
BTW - the big ‘in’ for PS in 3D work is for a texture artist to work natively in PS by loading up other people’s models, and editing textures in a 2D environment. You can see the materials in context, open them and use all the tools in PS, then save and reapply them. Other things like rendering, lighting, etc. are ‘perks’ in this context, imho.