I don't know what sewing blogs you're reading, so I don't know just what you mean by "expensive fabrics and couture techniques."
Nice fabrics are all well and good, but a) you don't want to sew nice fabric before you feel your technique will do justice to that fabric and b) nice fabrics can be gotten at major discounts, especially if you're not looking for something incredibly specific. My favorite is FabricMart (fabricmartfabrics.com).. I've gotten some really nice stuff from them at really really great prices.
Also, when someone is critiquing their own work on their blog, or even somebody else's, part of the purpose of that is to look at the details and consider what could have been done better. It's not necessarily a value judgment on the already-finished garment-- it can be a reference for the next one.
And one of the biggest things people are usually looking at when talking about the quality of a garment is the fit. Most sewing blogs are very disparaging on RTW clothing. That may be because people are more inclined to sew if they have trouble buying something that fits, but it should also put some perspective on the general criticism.
I don't know just how many people take classes, but most do read books. And tutorials.
I love old sewing books. They tend to have a lot of information, a lot of technique, and they're nice and cheap!
The whole "couture" thing is.. complex. Theoretically, "haute couture" is the dressmaking equivalent of bespoke in menswear-- made to measure garments built from the ground up for a particular person. But "couture" has become a bit of a buzzword. It seems to be used a lot to describe any technique that would be time-consuming or "advanced" or focused on detail. And then to some extent when a blogger refers to something as a couture technique that may just mean that's what it was referred to wherever they learned it. I think newer books refer to a lot of things as couture techniques that would be covered in older general sewing books but not called couture. Especially things like pattern matching and anything involving hand stitching or hand basting.
Have you looked at any of the more beginning sewing blogs? One of the neat things about sew blogging in general is that people can chronicle their own progress, and at the same time, get some feedback and advice on it. And blogs can be a great way to LEARN some of those "couture techniques."
Jilly at JillyBeJoyful just did a "Do you have mistake-o-phobia? Do I?" post http://jillybejoyful.blogspot.com/2011/07/do-you-have-mistake-o-phobia-do-i_18.html
She also did some great welt pocket tutorials awhile ago.
Then there's dfr at Sewing Miss Adventure http://sewingmissadventure.blogspot.com/
.. Erin over at the Amateur Sewist (http://amateursewist.blogspot.com/
) has been doing mostly home dec stuff lately because she just moved. Gloria at GloriaStitches (http://gloriastitches.blogspot.com/
) sews sometimes.. and it's always exciting! Those are mostly the PR chat crew.. 'cuz they're who I know..
Then there's the Slapdash Sewist (http://theslapdashsewist.blogspot.com/
).. Rebecca over at Tales of a Wannabe Seamstress (http://talesofawannabeseamstress.blogspot.com/
).. Sew Silly (http://kimsewsilly.blogspot.com/
) .. Yarndiva at Sew Old Sew New (http://silkmothsewing.blogspot.com/
) who commented on one of my posts awhile ago and I followed her back to her normally-sewing blog to discover her pickling recipe.. and now have a crock of pickling cucumbers pickling in my fridge.
I've been blogging more about gardening and pickling lately.. that time of the year.
I hope some of that was helpful.. and that I didn't leave too many people out..