From what I've read about Tonic, they have a lot of tech for Powerpoint compatibility--in particular, reading Powerpoint files, writing powerpoint files, and converting them into file formats which do not require powerpoint.

Slide.com doesn't do anything with PowerPoint. If you go yo Slide.com, you can see that they are not a presentation software company; they are a social networking widget company. Slide.com is not about technology--in fact, their tech looks downright trivial. They are all about branding. Slide.com has no technology to buy; they only (maybe will sometime) have customers to buy.