I really hope your post will get more future affirmation, I personally Bookmarked it.
For AV malware tests, I absolutely understand using a VMware environment, but for everyday assessments at times posted here, I don't think is gives a full picture of a AV's performance and system impact without all of the other variables mentioned in point #2 as well as not using all the PC's RAM and CPU resources. Even though the difference may be negligible, I still like "real world use" feedback better, but, I understand for general test driving of the AV's settings, malware protection etc. there is no better option but from within a VMware workstation.
But granted, everyone is using a different device set up (RAM/CPU, running software etc.) so that can be a factor in how it may perform differently on our personal devices.