The full answer to your question is complicated, but I'll try to sum up the relevant parts. Basically, it's a combination of the scope of your project, and how quickly it must sell in order for you (or your company) to survive.
The easier part of your question is development. It's pretty easy to understand how the bigger the game you want to make, typically, the more developers you need. You can trade off between expensive senior developers who (hopefully) do more per person, but spend less on management and other supporting services.
Publishing is primarily about 3 things: funding, distribution and marketing.
Funding also has a relatively direct relationship. If you have a really small scope project, then funding can be living off savings. As the scope increases, funding can expand to friends and family, angel, a milestone-driven publishing deal, venture capital, or a partnership / acquisition. Usually, the more money you need, the more you have to trade off (ownership, profit sharing, etc). You're asking someone to take more risk on your behalf (you may never finish), so they get more of the potential take at the end.
Distribution must be chosen carefully depending on your intended audience. Making an indy PC game? Steam is a decent choice. They take a straight 30% per copy sold for a pretty commanding global distribution system. Making a mobile game? Apple Store also takes a 30% cut. Both cases do not guarantee that your game will even be advertised anywhere so it may stay buried unless there is some other way people become aware of your game (news, blogs, featured game lists, etc).
So, if you are making a 1-2 man project: ex: you as a programmer / designer teaming up with an artist, then you can potentially live off savings and publish through Steam / Appstore. If you want to propose the next epic FPS and need 100 artists, programmers, designers, producers, audio, and tech artists, then you're going to need to convince someone (usually a publisher) to give you money. Then you have your own independent company that develops the game. For example, Bungie @ Activision, Respawn @ EA, Insomniac @ EA, etc. Some games are internally published when the development studio is owned by the publisher, such as 343 @ Microsoft. Some games are internally published when the development studio is THE SAME company as the publisher like Riot. Some games like Darksiders is published (development funded and distributed for console) by THQ but the PC version is distributed by Steam / Valve. I believe Minecraft was initially developed alone by Notch then self-published / distributed as a download through their website (I could be wrong here), but is now distributed through many channels. There are a lot of different combinations and options inbetween that makes it seem more complicated.
I don't know how to explain that in a shorter way at the moment, but hope that helps!