The problem is that there are huge swaths of use cases that are not covered by the current rss standard. For example, want to use standard RSS for your video feed? Ooops! RSS does not support thumbnails, duration and a bunch of other features.
So everyone goes ahead and makes their dialect of RSS and pushes that. Apple did this with iTunes and so did YouTube.
What clearly needs to happen is that RSS needs to have a refresh. The common uses cases need to be integrated into the standard.
“Dialect” implies that this is ad hoc, but the RSS 2.0 standard specifies a way to extend the format and that is through namespaces, which is exactly what Apple does with the iTunes namespace. This is a good way to extend the format IMO: no breaking changes and the opportunity to grow.
In practice the incompatibility comes less from new invented fields (that happens rarely and when it does it has a namespace attached to it most of the time), and more how certain fields are interpreted, which fields are used, etc. Something as simple as showing a short summary of an item varies significantly by player.
So everyone goes ahead and makes their dialect of RSS and pushes that. Apple did this with iTunes and so did YouTube.
What clearly needs to happen is that RSS needs to have a refresh. The common uses cases need to be integrated into the standard.