Just HBO NOW, not HBO GO. HBO NOW has been really disappointing. Their service cannot handle the load when popular episodes get released, and often the quality of streaming is much lower than what could be supported by end users' connections.
Hard to say for sure, but since HBO Go is tightly coupled to cable companies - I would guess its distribution model is as well.
I can imagine a cable operator centric replication model for Go, where HBO doesn't handle customer delivery at all. Instead their library would be replicated from HBO to {Comcast, Cox, TimeWarner, ...}. Each HBO Go customer ID would be assigned a "master cable operator" responsible for their delivery and managed centrally, but HBO would feed customers links to operator-local content replicas.
In the common case, customers access HBO Go from within the operator's network so transit is free and HBO is totally out of the data path (just catalog/user interaction/etc.). But the service can still easily support remote access by going over the public internet.
The benefit of that model is HBO controls the catalog and most of the user interaction, but doesn't need to build/provision/pay for a CDN which scales with # of total HBO subscribers across the entire world (and guarantee reliable connectivity from their CDN to every customer). They just need to replicate their library across a few tens of cable operators who are able to keep everything local. Plus the entire sales/marketing/billing models are completely different too.
Thinking about it from HBO's perspective it makes a million kinds of sense if you have the majority of your customers paying for you via the broadcast cable subscription model. OTOH, with HBO Now there is no cable operator in the picture so they can't make that optimization and now have to build something which looks more like Netflix.
HBO Go doesn't stream from the operator that you sign in with, it streams from nearest node. I am temporarily living in a place with Time Warner cable but I sign in to HBO Go with an Xfinity account. The stream comes from Time Warner. However, if I watch through xfinity.com, it comes from Comcast (and the bitrate is much lower).
My understanding of the situation is that Go really wasn't able to handle the load being asked of it, so HBO looked to build a successor. They ended up outsourcing it to MLBAM.
I have never had any such issues with HBO Now. Maybe it's more of an ISP peering issue. (That is, if you get Internet access through your cable company, I bet they open the floodgates for HBO Go and not so much for HBO Now)
Trying to watch Game of Thrones at release time on release night is mostly a nightmare, and I'm glad I didn't try and organize viewing parties because they would have been failures. The HBO NOW subreddit[1] is full of unhappy threads, and at least on one occasion, the error message presented was definitely indicative of an overloaded server[2].
It gave me that error even after logged in. Whatever they do to validate your session token every time you try to watch a video also goes through that server. If it keeps you from watching videos even after logged in, it doesn't matter that it's not the video server itself.
Besides a minor UI bug in their video player which I didn't really care about, I've never had a single issue with HBO Now. (Including GoT on release night)
