What you said is is way more reasonable than what the original posting said. The original posting referred to "platforms without a default client," whereas you

What you said is is way more reasonable than what the original posting said. The original posting referred to "platforms without a default client," whereas you refer to, roughly, "a commonplace convention for some higher level platform to select a default client" (my words). The original posting further implied it is a problem that there are "competing choices for feed readers," which you did not state. (This was silly, not least because the counterexample of Twitter also has competing choices for feed readers.) I completely agree that stronger RSS choices and less asking the user, especially at the browser level, would be a great thing. More defaults would be great. But the original post was supporting the idea of a single, global default vendor.