I'll have to disagree to a certain extent here.
The question at hand is, "Does Quality Control Exist?" The obvious answer is, Yes. Of course it does. No model company in the world could remain in business more than six months without having Quality Control. The real questions should be, "How good is Quality Control for company X or company Y." and probably more importantly, "How much will it cost and how much are modelers willing to pay for a model that is 99 - 100% accurate to scale, has a guarantee that there are no errors in the instructions, and has abosolutely perfect fit on all parts?"
It has been stated here - and it is true - that it all comes down to money. Companies in today's market cannot get away with the things they did 10, 20, or 30 years ago when it comes to problems with quality. But even the best companies will have occational errors that slip through the cracks and must always balance their Quality Control efforts against their profit margin. After all, they are are not in business JUST to make good models. They have to make enough money to pay employees, acquire raw materials, pay for utilities, dedicate funds to R&D, pay for marketing and advertising...the list is very long indeed.
We've all either had a horror story or heard about one from someone concerning problems that should have been corrected in Quality Control. Problems that cannot be corrected simply by the modeler are not acceptable and should not be tolerated. Some problems are so bad that it's amazing anyone still buys the kits involved. But all-in-all, model makers today are doing a pretty good job (IMHO) when it comes to producing a quality model kits at a fair price.
Is Quality Control as good as it can be? It varies from company to company and dramtically varies when talking about kits produced 10, 20, or 30 years ago. Can Quality Control be better? In some companies, yes. It can and should be improved quite a bit. In other companies, Quality Control is pretty darn good and only needs a little tweeking periodically to keep the standards high.
Here is my own take the issue. I would personally rather buy a $30 kit that requires a litlle work than have to pay $100 or more for an absolutely perfect kit. Now, would I rather have a $30 perfect kit? Of course I would, but I don't think it can be done. Not in todays marketplace. For the prices I'm paying, I can gladly accept a few minor errors in the instructions or minor problems with parts that will require me to do a bit of sanding or filling. I am exceedingly pleased that many companies are now producing kits with virtually no errors for an amazingly inexpensive end item cost. I hope this trend continues.