Just think about it... everything (other than broadcast discovery) is http so the path through the network is fairly clear but with SD's apps and DVR, the DVR is the "source" of all client streams (unless a legacy tuner or DRM - as the DVR does not support legacy devices (probably never will) or DRM (currently, expected there will be support))
First though you seem sure about
For instance, when I watch something live OTA, it's pretty straight forward. The bits must go:
Antenna -> HDHR Connect -> [ethernet] Router [wireless] -> HDHR Viewer app
If you have the DVR and are using SD's apps, that is wrong as the DVR is used for live to be the buffer so it actually goes Antenna -> Tuner -> DVR Engine -> client how it gets from the tuner to the engine and the engine to the client depends on equipment between (i.e. back to router if router is your wireless access point and the clients are wireless)
For your second example the recording is on the DVR so a http request is sent to the DVR engine which responds through the network... the tuner isn't involved as it isn't the source of the content.
For your 3rd (PTV) situation, the source of the content is online so from the cloud it comes to your network through your router to the tuner as a tuner on the device serves the content as if it were coming through the antenna. Again, if you have SD's DVR, the playback is through the DVR to act as the buffer and the client essentially connects to the DVR engine.
If you have the dvr, I recommend the tuner and the DVR be on the same switch (as well as any wired clients- you can have switches in between if you like... generally people should limit to 3 switches between the path, but some feel that is an antiquated rule) and that no wired device connect to the router other than the switch. I suggest your router be in the path only for internet traffic, however for most the router is also the WAP so most likely wireless clients connect to it but personally I recommend a separate WAP and leave the router to function as a router which is used to interconnect networks (i.e. "gateway" to the internet).