Gosh, there are some wonderful comments here, and I would actually like to propose two items which having read all of the above statements, and the mixed messages being sent regarding reviews,

I would like to, if possible, interject a little reality and to also provide some ideas as possible solutions.

First as @Justin Tadlock Stated,
First, I want to say that in the past, I got many “anonymous” 1-star reviews by users who didn’t like that I wouldn’t customize something for them for free. I was even told as much by some of them. So, I’d naturally add a 5-star review myself to counteract that kind of crap.

Why are plugins created? 1/2 of the time, they are created in hopes people will like them, the developers became more visible and are able to sell other associated services and plugins. The other 1/3 or so they are created specifically for a singular purpose of the authors and they put them out in the plugin repository so if others want to use them they are able to, but the author in no way expects to nor willing to do anything in the way of tech support and maybe or not updates, But the dev shouldn't be punished because he/she works full time and put something out there to share with other devs.
At the same time they should not get a bad rating based on the above issues, that's just punishing a person for their generosity.

1. I absolutely agree with @DavidCoveney, his assessment is right on. AND it goes directly to the heart of the matter. The Developer that is keeping his plugins up-to-date, the most dedicated will surely get the higher ratings this way, and well deserved ratings too.

2. Peer Reviews are essential, as stated above, but there is a huge discrepancy in both a users ability to use the plugin itself (although truth be told, they are supposed to be dummy proof right?) and the users ability to accurate rate the item, whether or not they are an employee, affiliate (don't forget affiliate marketing, sales on other items the author could be selling)

So in thinking about this, and the continued sucess of wordpress, and the almost obscene amount of users, developers, promoters, advertisers it has These days in relation to say, oh 2004, it would seem maybe a step in evolution is the solution for the issues.

By that, I mean two types of plugin-repositories:
1.) for those dev's who just put it out there to be nice maybe giving a link to their git-hub repo if they wanted, but no review system as such a simple thumbs up and "Thank you" or not.
This would have clearly distinct, visible statements of "no support unless I get a few extra minutes, it's not about pay, It's simply about 'sharing with t my community items which were developed for myself, if you can get any use out of it, go for it.
( maybe we could develop a specific logo to put on this type of module) Sharing is Caring :)

2.) Have a Repository as it it now, only clearly state to folks, these are free modules which might have additional paid for functionality included in promotion and/or support of their WordPress focused business. (basically a business directory) and support is provided for either free or paid at the times specified by the developing company.
Basic Business info is setup when by uploading a new plug-in, A company profile, just basic, hours of operation and maybe a 'badge' for yearly participation.

Two sets of Guidelines Used
Novice, Intermediate, Expert <--Ability required for non-help install/setup/updating of the module rating system 1-5 of the business AND the employees, affiliates of those associated with the company.

Another Set Equal to that above, only given buy those who download and install it.
Not only would this facilitate development in the future but it helps to bridge that gap between a computer literate and computer non-literate user which is what WordPress is pretty much all about.

A legend which clearly states what each number equates to in the scheme of things, or better yet, a slider next to the radio button that puts something on the low side or the high side, then you could define actual question:
1. Did this install easily and without help or modification?
2. does the plug-in function as stated it would?
3. Would you recommend this plugin to your friend?
Comments:
(required)
I would personally find this infinitely more helpful than a star.
This would give much more information to the developers for future plug-ins,

That's my two-bits or maybe 6bytes of #justsayin
except that:

Evolution is a good thing, so is change sometimes. WordPress has evolved in every single area, well, exploded would be more like it, except the plug-in repository. So maybe it's just it's turn.

You could even randomly select 5 members to evaluate the module as contrast to the companies evaluation of itself. There's enough members who would participate I'm sure.
But ratings should be "blind" i.e. they don't see the developers information they are rating and those giving them should always be rotated. Module is upload and auto emails get sent to 5 random folks who volunteered for it.