Be careful who you say that around. Plenty of people aren't happy that Profession isn't a skill in 4th edition.
I didn't say it wasn't important to me, just that it wasn't important to 3e. That is, little effort went into constructing wage-earning rules for 3e. At the opposite end of the spectrum, consider GURPS, with its job tables.
So do cooks. Who are also called out as an example in the Profession skill description. Simple mathematics tells you how much someone with Profession (Cook) +1 can earn by practising that skill, and it's a lot more than 1sp/day. Consistency in this regard would be desirable.
To me, this is just a case of simplicity. The rules don't offer more than that level of detail because that level of detail at cooking was not engineered into the game. You are incorrect that this is a simple exercise in mathematics; the skill actually says
You can practice your trade and make a decent living, earning about half your Profession check result in gold pieces per week of dedicated work.
That word "about" might mean, in many cases, pretty much exactly. But it could also mean you earn a fixed salary commensurate with your skills. The GM could also says that it means "it depends." For instance, a week of dedicated work could mean a week of work at your professional level. Regardless of skill level, the GM is free to rule that regardless of skill level, the village baker makes 2 gp per week. Perhaps to make the full amount, he needs to have access to a high volume bakery, or a wealthy patron, or be near a large city where he can command higher prices and participate in fairs. The word "about" is not very informative but it does tell us one very important thing: the mechanic is an approximation and the GM is being asked to adjudicate an appropriate result.
I tend to the belief that the economy is one of the more significant factors when it comes to world-building. And I'm easily annoyed by rules that are an obvious afterthought or that are inconsistent from place to place. Although it's probably right that a functioning economy is a detail when it comes to a game about hunting monsters in dungeons, not every game is like that.
I think economy is important, too. It annoys me that the DMG claims a large city has a billion chickens for sale if you can afford them. But simply because some of the rules don't work well as one might hope does not mean that
1) the rules don't exist, or
2) the rules aren't intended to cover the area, or
3) the GM has lost their usual prerogative in dealing with situations not well covered by mechanical expressions of the rules
Simply because 3e is not particularly good at running SimBarony doesn't mean it can't simulate an imaginary world full of ordinary workers and laborers, protected by a military aristocracy, and supported by a population of freeborn tradesmen and hirelings. If you want nitty gritty detail on various Professions, you're going to need a sourcebook for that. Just because the DMG doesn't have good rules for ship-to-ship combat between flying ships doesn't mean that the game universe falls apart like a broken toy if you include them.
If you want more detail on running a business, guess what? The DMG II gives more detail. Sadly, it doesn't revise some of the broken guidelines in 3e. 4e certainly could have done that; instead, the designers of 4e decided to peel off any semblance of a game world economy and set it aside.
4e can be run at a high level of simulation; there is nothing preventing you from doing so. But compared to 3e, first you have to craft on a mundane economy of some kind, replace the rules for making, buying, and selling items, come up with some kind of background or ecology for any and all creatures encountered, etc. 4e's world is more of a facade. For that matter, it hardly examines why such a thing as "starleather" is so consitently available and why it has a stable market price. That's 4e for you. It's not necessarily bad. The Final Fantasy games are full of things with ridiculous and arbitrary prices and you can still play and enjoy those games. You would find it difficult, however, to adapt that kind of aesthetic for a supposedly consistent gameworld.
Can the 3e economic system be improved, while still retaining its basic simplicity? You bet. Will your game world break if you used the posted guidelines? Not necessarily, although I would watch out for the billion chickens. Does that have anything to do with magic or feudalism or any of the above topics? No, at this level, we are simply talking about the utility of specific rules.