"I would ... say that all these modules are useful for web development."
It's very unusual for a web developer to work directly with RubyInline. It's quite a stretch to classify it as a "web development tool" or significantly related to "Web Apps."
"I made almost immediate comparison between the two"
It's not even close, though. The Ruby analogue to WSGI and Paste is Rack, not Mongrel. RubyInline and Psyco are very different things. HPricot is one of multiple options for HTML parsing in Ruby (nokogiri, scrapi, scrubyt). There are multiple JSON options for Ruby (including yajl bindings), and half the paragraph is about simplejson vs python-cjson, which has nothing to do with Ruby. There are also multiple Ruby templating systems available (erb, erubis, haml, markaby, liquid), but you only mention python templating enigines.
And all of these are just a small subset of libraries that you can have in a typical web app, such a small subset that they aren't really representative of anything.
"You never curious about hot-and-shiny key value databases for work?"
There are a whole slew of libraries for "hot-and-shiny" data stores (there are at least 5 Ruby libraries for couchdb alone) and it's not uncommon for people to roll their own. I don't think shove even supports anything "hot-and-shiny" like couchdb, tokyo, cassandra, etc.
"The best way to know about these languages is to use it to hack on something."
It's very unusual for a web developer to work directly with RubyInline. It's quite a stretch to classify it as a "web development tool" or significantly related to "Web Apps."
"I made almost immediate comparison between the two"
It's not even close, though. The Ruby analogue to WSGI and Paste is Rack, not Mongrel. RubyInline and Psyco are very different things. HPricot is one of multiple options for HTML parsing in Ruby (nokogiri, scrapi, scrubyt). There are multiple JSON options for Ruby (including yajl bindings), and half the paragraph is about simplejson vs python-cjson, which has nothing to do with Ruby. There are also multiple Ruby templating systems available (erb, erubis, haml, markaby, liquid), but you only mention python templating enigines.
And all of these are just a small subset of libraries that you can have in a typical web app, such a small subset that they aren't really representative of anything.
"You never curious about hot-and-shiny key value databases for work?"
There are a whole slew of libraries for "hot-and-shiny" data stores (there are at least 5 Ruby libraries for couchdb alone) and it's not uncommon for people to roll their own. I don't think shove even supports anything "hot-and-shiny" like couchdb, tokyo, cassandra, etc.
"The best way to know about these languages is to use it to hack on something."
This is very true.