I read through this post David Allen's Universalism and I think this person totally misses the point of GTD. For me GTD is about capturing all my ideas, big and small. Buy toilet paper is a small widget-like task, but it is still important. Since I have a place to put all of my ideas, I find I have more time to focus on the "deep work" this person claims is lacking from following GTD. Since I have a trusted system, I can forget about buying toilet paper and focus all of my attention on the hard problems. Just as an example, there was one time there was a nasty bug causing random crashes in our software. For over a week several people tried to find the cause and failed. They finally asked me because even though I knew nothing about this particular code, I'm good at debugging. I set aside my next action lists and spent 8 hours working on this one bug and I finally figured it out. I don't know if GTD was the reason, but I knew I could put everything else on hold because I had a trusted system to go back to the next day and pickup where I left off.
You also don't know when you will a eureka moment. Sometimes I'm in bed reading a fiction book and a solution to a problem that has eluded me just hits me like a bolt of lightening. I put my book down and pickup my iPhone to capture this idea, then and there. Without a trusted system, these ideas can get lost. I can also pickup my book and finish my pleasure reading knowing the idea is safely captured.