The "web" as in Tim Berners-Lee(TBL) "world wide web" is http+html which is "documents".
Saying TBL-web is "best as a document platform" makes perfect sense. It was defined that way therefore, use it that way. It's tautology.
Back in 1993, if we want to say "X is best though of as a network app platform" we'd have to use the word "internet" instead of "web" for "X" to be conceptually pure and technically correct (the best kind of correct.).
But now we have things like Dropbox (and thousands of other "web apps"). Dropbox runs on "http".
Dropbox "syncs". Syncing is an app. Dropbox is an app. Dropbox runs on http. Http is "the web". Apps run on the web. The web is platform for apps. That's the reality of where we are today.
This is they beauty of the network communication protocols.
It is is just a consequence of what network protocols happen to be open by default.
It's about the evolution of how society sees the web and not about what its original purpose is.
Dropbox uses html and http. Drew Houston and his team are not going to submit an RFC so that the internet has a new protocol and port "dropbox://myaddressoffiles:8675". No, Dropbox the application will just use "http://". It's because they did not pursue conceptual purity of having "dropbox://" that allowed everyone inside and outside of corporate networks to use the service and share files.
That is "the web" we have today and in that scenario, the non-technical use of "web" includes the underlying internet stack to make web apps possible.
What's the alternative? Tell millions of Dropbox users that such a service is outlawed because "the web is best as a document platform?"