They are the same except for the size. Pelagic makes the guts and then Oceanic put their stamp on some. Same for Aeris and I think Sherwood. But to answer the question, Oceanic used to make the data 100, and a bunch more computers along with the SPG and they all fit in the same boot, so no matter which setup you had, you could use the same boot. Upgrade the computer, no prob, just pop it out, put the new one in. They got rid of all the lower end computers about a year, year and a half ago and started making the Versa and Versa Pro. They were bigger diameter than the old style and had their own boot. So, if you wanted the Versa, you had to buy the versa and the boot and usually the SPG because no one wanted to break up the set. This didn't set too well with people, I know it didn't set to well with the shops when they had to deal with people that just wanted the computer. I think Oceanic figured this out pretty quick and came out wit the Veo 100 and 200 which are back to the original "hockey puck" style and fit in the old boots. So if you had a Data100 and wanted to upgrade all you have to do is buy the computer alone and pop it in your old boot.
In short Versa=Veo100 and Versa Pro=Veo200. The ONLY thing different about them is the look - functions, features and ability are exactly the same.