Absolutely nothing. Technically, it’s strictly worse. People even added other namespaces to patch up some of its deficiencies, e.g. <content:encoded>.

I think the reason that RSS is used can be summed up as: Apple is lousy at developer relations.

They didn’t invent podcasting (name or technology), but they were the first major player to do stuff with it. Although consensus was already strong that RSS was technically terrible and Atom had existed for over a year (though it was not finalised) and was even fairly popular, Google especially having embraced it⸻ Apple chose the old-and-inferior RSS as their foundation. And then stuck their heads in the sand and didn’t talk to anyone, ever. Because that’s Apple’s style: throw stuff out there, let people do what they want with it, don’t attempt to be a community leader.

So what did everyone else do? Feeds had to be RSS, of course, to appease Apple. And then other apps implemented RSS, just RSS, like Apple had done, because what’s even the point of using Atom if it won’t work on the biggest platform? General-purpose feed readers didn’t have much specialised functionality, and had a few major players and a long tail of other clients; it was a much more well-distributed field, all things considered. But podcasting was, as I understand it, much more only one player for a while, then only up to two or three; and it depended on more specialised functionality. So it was never as democratic as general web feeds.

Over time podcast feeds ended up a horrible mess of repeating the same logical field 3–6 times in differently-named elements for different platforms, as they all added their own namespaces and mostly-identical-but-sometimes-slightly-different data fields¹. Because people were using it as an actual data format with domain-specific fields, they were more likely to just use an XML parser and talk just RSS, rather than a feed library which would be RSS-/Atom-neutral.

I believe that at some point Apple did implement Atom (not sure when), but it was too late, too much other stuff didn’t support it and so no one used it and so they ripped it out again a couple of years ago, and podcasting is set in stone using the inferior RSS.

I should write this up further at some point: the tragedy of podcast feeds.

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¹ This stupid pattern can be seen on the web too. <meta name=description>, <meta property=og:description>, <meta name=twitter:description>, something in a JSON+LD block…