Well, the game wasn't designed for you to need top d-grade equipment at level 20. Sure, it would make your leveling easier, but when we all first started, we used NG and low d-grade stuff well in our low 30s.
I've heard this before and it's not exactly true. Yes, the game is designed so that you normally *don't* have gear until well after you can use it. BUT, this is assuming that you are playing the game as the designers *thought* it should be played. Thus nukers can do OK with sub-par gear solo, archers in small groups and melee in larger groups.
And when the game was 'new' and everyone was roughly the same level it was more or less true. (Barring the usual balance/skill idiocies you see in all games.) Now? The majority of players are higher level and even their alts/subs are higher level.
When it comes to solo play to 'catch up' with the other players this mob > (melee) player gear imbalance is pretty obvious. It is bad enough that the devs were pretty much forced to add more 'aids' to solo play such as instant herbs and soon to come 'temporary' weapons in interlude. (If you've played Diablo 2, think 'ethereal'.)
With that said, all isn't doom and gloom, although I think the 'cash makers' of the past are changing again as servers mature.
First off, those who tell you to 'play the market' are living in the past. With the vast majority of people IN A grade and even S grade, the 'boom' market of materials is cooling down. This is good and bad.
Bad because making 'mad cash' overnight from selling overpriced mats isn't a 'sure thing' anymore. And the Ol' buy cheap, sell dear isn't as probably as it used to be.
Good, because it means the RMT style prices are deflating fast and more 'affordable' prices are taking over. As well, cheaper mats mean crafting for use becomes cheaper and more appealing than selling mats and buying overpriced. It also means that a lot of the pressure on the manor is lowered, and it becomes more accessable to those who do need it.
Of course each server's market is a bit different, but from what I've seen even the most crowded servers are 'cooling off'.
Playing 'casual' isn't impossible or even 'hard' really though. You might get less out of 'politics' or sieges than the more 'hardcore' but that doesn't mean the rest of the game is any less for it. (And to some extent, avoiding those who do is it's own reward. =P ) It may take longer to 'get there' but as long as you play smarter rather than harder, I think you'll get more out of the road than those who rush though it do.
As someone who has been playing 'near casual' pretty much since Open Beta, I think you'll find that as long as you don't try to 'keep up with the Joneses' and simply play the game for fun, you can aquire the gear you want just by setting realistic goals and working towards them. By all means, making friends and being a part of a good clan can help that a lot, just be understanding that finding a good clan and being part of one is harder than just walking into Giran and shouting LFC!
Sifting through the player guide forum is a decent place to start followed by your servers forum if your looking for ways to make cash. But here's a few extra tips to get you started.
1)To make cash, level SLOWER. That means green/white mobs and grinding the available quests as much as possible.
2)Use your seven character spots wisely. Handing down gear and leveling another char helps break the grind, lets you try out new classes and adds extra cash.
3)Before diving into the buy/sell of trading, take some time to learn what is more useful, what is useless and what the difference is between the 'NPC price' and the 'market price' of materials and gear.
4)Know what is purchaseable from NPC's and what is not. Giran NPC shops sell the highest D grade and C grade gear you can buy from non-players, and the Blacksmith of Mammon can upgrade your weapons up to top C.
5)B grade weapons are probably going to be your first real 'sticker shock' as they are currently on the the hardest to get/craft. (The drop/spoil/quests on those are still pretty bad.)
Good luck!