I'm with vbampton on this one. Even if almost all contexts are always available, you can still get a lot of value out of them.
Usually many contexts are available to me, too, and I look at all of them. They do help with focusing and batching tasks. If I don't want to make any phone calls right now, I can close the list and don't look at the phone calls I could make.
I love my "Anywhere" list, where I put things I need to think about or brainstorm. Perfect list for my daily bus rides to and fro work and when going for a walk.
As part of my job I have to do a lot of copywriting, so I have a Writing context, which is my favorite list. I associate that list with "Yes! I get to write!" . I usually don't write in my office, so having that context made sense. I can sit outside in the sun or a quiet spot in the nearby forest with my iPhone, look at my Writing list and start drafting and brainstorming in an app, in my journal or on a legal pad.
Last week we got a new hardware firewall installed and I had no access to the internet for the whole day. I could immediately close the Online list and work on a couple of less important offline tasks without feeling guilty.
Also, I find that GTD is very flexible. If I want to try out a new experiment, for example "no contexts", it's easy to pull off with my list manager. It's never a 100% commitment and if it doesn't work out, I can quickly move back to contexts. You can have lots of creative fun with this!
The last few weeks where very fast-moving and it was easy to lose track. So I created "Weekly Wins" and "Daily Wins" contexts and put them at the very top to help me stay focused. I asked myself "If I got to the end of the week, looking back, no matter how hectic and stressful the week has been, what do I want to be true in order for me to be happy with the week?". Now that I don't need it anymore, I deleted them.