Who are google to define "quality" and refuse to list sites they deem "not quality"? If a site is poor quality it will die all by itself in time, unless it's a spammer.
Google are a search engine. They should return the most relevant results they have, not the prettiest. If they have a spam problem that's their problem not ours - fix that and get on with things: it's easy enough to determine the real baddies from IPs and domain registrations plus a bit of serious searching by their own SE. Unfortunately, that's partly why the internet is collapsing: no one wants to kill the cash-cows.
If I go to a site that gives me what I want I may think "not very well made" but I still use it. I even used to use google for searches, despite the SERPS having some of the worst technical problems I've come across. There are loads of errors per page and their general quality (results AND layout) has become abysmal!
When it comes down to it, a lot of small sites have been making a lot of customers, ecommerce- and information-seekers, happy for several years (I have entries in a directory to confirm this, plus customers of my own). And google now tell us we shouldn't use those sites any more?
I stopped using google for serious searches over a year ago, apart from the occasional research of google itself; and I log into Base once a month for a single customer's froogle which I would prefer not to do.
I wish I could block google in robots.txt but I can't because my own customers and their customers would complain. But one day...
Google is obviously killing (or trying to kill) a lot of useful sites. It has no reason to, apart from hubris and the general arrogance of graduates who think they know how the world works. They never do: it takes years of living!
Of course, they will not recant. How could they?
One consolation to those of us once-google-philes now disillusioned by google: for every person put out of a job or even disappointed by google results, a dozen or more people will move to a new engine; they will also tell their friends. That's how google got built, that's how they will die. Soon, I hope, but I fear it will be later.