They could use Linux or Mac for servers. That's a big deal for many companies.
Plus, more tools that are used during developer/deployment/etc are open source.

>
>What incremental benefit would the end user get if they brought it up to the current version that would match the magnitude of the benefit they got by going to ASP.net?
>
>They got a major benefit by this move.
>The reason this app has survived since the CPM days (one of very few) is that the authors picked good inflection points and patiently waited for them.