In reply to PolyWogg.

"But if they simply offer the customers a viable migration tool, which they can offer pretty much to anyone without the original’s help (albeit more easily done), people will migrate anyway. Why pay someone to steal their customers that will likely come their way for free anyway?"

I'm not an expert on acquisitions, but if you buy the plugin you can then reach the users directly, via plugin updates, email newsletter, etc.... i.e. much better conversion rate that what you are suggesting.