Hi KC
There is an element of truth in what he is saying but it is all relative. It also depends on what emphasis you put on the word inferior.
With lens there are a number of rules of thumb which in general are a good guide but there are exceptions to these rules. i.e a Prime lens is generally better than a zoom mainly for two reason. One is the primes have less glass elements so inherently has an advantage. Two the designer only has to be concerned about one focal length as opposed to keeping the performance over a range of lengths. This does not guarantee that a prime will be better than a zoom because there are poor models of prime about.
Likewise a x3 zoom is generally better than a x10 zoom. But if you spend enough money on a x10 you can get some pretty decent lenses.
So if you compare an IS to a non-IS version of the same lens generally the non-IS has the edge because it has less glass elements. But if you handhold the advantages of IS takes over from the non IS.
What it pays to do is source good lens reviews based on professional opinion and bench tests as opposed to some of the reviews attached to shopping sites. The shopping site reviews are based on the reviewer's terms of reference which maybe he or she would not know a good lens if they fell over it. Plus opinions tend to vary wildly from excellent to rubbish.
This site has a large range of lens you can compare - the higher the numbers the better the rating
http://www.photozone.de/active/survey/querylens.jsp
Fred Miranda site is a well respected site
http://www.fredmiranda.com/reviews/
Also The Digital Picture
http://www.the-digital-picture.com/Reviews/
You will quickly get a consensus from these sites if a lens is Good, average or poor.
I am sure other members can add to this list of good quaility review sites.