What you are saying is definitely true. It always depends on the book though. Most reviewers simply cannot review every book that is released and that is totally logical considering the amount of time that needs to be spent for reading them and then writing a review about them and all of that fast because the next batch is only a week away. So they have to pick and choose and some books just get away more favorably than others.
If you want an example you just have to look at All-New Wolverine. Every issue besides #6 has at least 5 reviews so it definitely has a good sample size.
Something like X-Men '92 is the exact opposite and I have already touched upon that in my original post that I plan on removing it if I should do something like this again.
That UXM in this particular instance has a small sample size and a ravaging one to boot is unfortunate but there is nothing we can do about it. If you want to you can see it as a rating in itself that so many reviewers don't feel compelled to write their thoughts about some books.
As a possible warning I could point out small sample sizes like this next time though. That being said comics are a niche medium that also has a weekly release schedule. Every issue of every series getting like 20 reviews is just not happening for reasons I have already said. While 1 or 0 reviews are obviously problematic I find 2 or more to be perfectly acceptable for a series that has been ongoing for over 6 months. If anything that is just the status quo on the comic book market for better or worse.