I'm going to go out on a limb and say that most people who are bothering to read a dominion strategy forum on the internet have played enough to understand basic concepts like the power of putting curses in to their opponents decks; the rote beginner is probably not ever going to read any of these articles. I'm guessing that people who are reading like articles like are reasonable dominion players and want to get better, in which case they should, in fact, be carefully considering all the possible synergies when they draw their opening hand.
Back maybe a month ago I was surely not at a level where I could understand all of the dynamics of the game, and the friends that I play with still occasionally make clearly suboptimal opening decisions (e.g. opening Remodel in a kingdom with no good targets, ignoring Sea Hag on boards where it would be very strong, etc.). I think it's erroneous to assume that all individuals who read a Dominion strategy forum are extremely adept at the game, or to assume that experienced players are the target audience; if that were the case, there would be nothing to talk about.
ChaosRed's post is also a good counterexample.
Edit: As for the sea hag vs moneylender debate, there really are enough cards that are very good against sea hag that I would definitely not be comfortable calling it better than moneylender a "vast majority" of the time, whatever that means, especially considering that moneylender is a card that I want to have in my deck in most circumstances.
I can only think of maybe 5 cards off the top of my head that would counter Sea Hag to an appreciable extent, and even with those cards in the kingdom I would still open with Sea Hag just to slow down the opponent. Masquerade and Trader are probably the 2 cards against which I definitely don't want to open Sea Hag. Whereas Moneylender... is just such a weak option now. It's only marginally useful in building an actions engine and it's not a very strong complement to BM.