Regarding your edit: 

> However, questions "what of AAA, BBB, CCC that can do XXX?" is much more narrow and more clearly defined and thus the clear answer can be provided such as "None" or "Try DDD" instead

Personally, I find this even more problematic than to ask "what is available" because you are fully expected to read the documentation and/or try a product/tool/whatever in question before you can even think about posting a question on Server Fault. Really, a site like ours should be your very last resort, not the first one. 

Also, this is very much a moot topic because that was clearly not what you originally asked and what this meta-question is about - your question was in no way different then "what backup tool should I use".