Well this is going to be a heck of an introduction post.
To start it off. I'm Nero *waves hi* and I'm just getting back into riding. I wonder how to put this without tooting my own horn.... I'm very mechanically inclined, and I have "the touch" when working with fiddly things. For instance I've always been able to make my bikes shift properly. And now my next question will destroy all credibility that statement may have had. But here I go.
What makes the difference between decent components and good components. I can answer much of that question on my own.
The last sport I was involved in was paintball. It's reached the point that fashion drives the industry. And you end up paying out the nose to buy the good stuff versus the pretty stuff. However I can tell you exactly why I chose X brand parts over Y brand stuff every time. For instance, I buy Palmers regulators because they work best (as proven on a dyno), instead of cheaper, and often more expensive components that people seem to like more. I've never gotten a good explanation of "performance" for bike parts.
Brake are something that gives you immediate feedback if the lever is quality or not. A poor brake lever will flex all over, often the end of the lever with have a lot of slop in it, the adjusters won't stick in place.. The same goes for the calipers themselves. A flexy caliper just feels bad, and can bottom out the available cable travel from a lever. (I had this problem when I was riding crap bikes) It all leads to cruddy feel for the rider, and makes it easy to justify the price difference between the "so cheap you can't buy them" parts you find on a wall mart special, and decent brakes you'll find on anything above the $300 level. Though that does bring into question the more expensive brake setups out there... I'm not ready to talk disks though. :-)
Shifters are a similar story. You have direct interaction with them. Good ones have a very good mechanical feel. Bad ones feel mushy and vague. I've never had the problem with indexed shifters, but i'd put money on really cheap models not even indexing the right distances. But since the indexing happens at the shifter that begs my next question.
Derailurs. Why the huge price range? What's the difference (beyond weight and bearings) between a budget derailur (say a $20 shimano alivo) and the ones that you find in the $180 derailurs. (say shimano xtr) Same 9 speed range. The only obvious difference is that the "better" one has larger pulley wheels. I do understand the benefits of larger pulleys. Where does the other $140 go?
How about bottom brackets? A quick scan of bikeparts.com shows a price range from $8 to $170. I have spent money buying good bearings for different things over the years. Even going with ceramic components I find it hard to justify $170 on bearings, especially with something that is only spinning 90-150rpm. Where's the benefit? That said I have disassembled, and repacked the bearings on a bike that felt crunchy, and was in definite need of a new BB. What makes the expensive ones "that much better" than the cheaper ones?
Cranks confuse me a bit. I understand you want them as stiff as possible, so you don't waste energy flexing them. Only to hook them up to a fairly spindly piece of metal that goes through the BB. What makes a good crank? Once you have a sufficiently stiff crank, is it just weight that differentiates the $70 ones from 400 cranks?
Educate me. :-) and thank you for reading my post.