Sounds like you are trying to find reasons not to use open-source tools?
2 to 5 could be applied to either open source or vendor tools.
As for 1, historically this may have been correct, but the support for open source tools has come on by leaps and bounds in the past few years and in certain cases surpasses the vendor support (this website as a good example).
The open source tools appear to be just as good as the higher priced tools with all the bells and whistles. Have been doing extensive research for my company on the testing tools for us to stand up a QA section and have made several recommendations in favor of the open source tools (I use open source tools quite a bit and find good performance in them)
I have been using Selenium (need less to say it is open source). In terms of features there have been thing which we wanted to achieve but there was no out of the box solution for it. Like -
Data Driven Testing,
Automatic initiation of tests,
Automatic mailing of test reports
But I found other tools which were capable of doing this like TestNG, ANT etc. Point is - Open source tools might not have all the fancy which is available with commercial tools but we might be able to come up with same functionality over time. Also there might be high learning curve with open source tool but one can learn only when there is learning curve...
I don't know what is the situation in all parts of the world, but here we developed own framework for Web testing, which uses Selenium tools + custom solutions. This framework is already used by several people for helping testers to do their job.