Coding, once the mindset is developed, is easy for most people to become proficient. The job of a programmer is not limited to coding, however. I will preface that given the nature of the coding, it is possible to learn much of anything related to software as long as one has the tools. Indeed, much can be learned from a good mentor.
That said, the four year degree is not without its benefits. A good course load will serve on a silver platter things such as design skills, platform details, a few programming language, etc. In addition, many people would benefit from the extra course in formal writing or an elective in Accounting. These are not programming, but often working for companies, one would need to write a proposal (persuasive writing) or create expenditure reports (Accounting). These are things in which university/college does teach well.
Mainly the people that would benefit from 4 year college/university degree (beyond just having the "sheep skin") are people that are not naturally self-directed with their learning, or those people that wants knowledge and skill beyond just coding, particularly those that wish to eventually move out of the coding work into management, needs knowledge related to a specific industry, or wish to be less of a software engineer and more of a computer scientist.
I will note that neither being self-taught nor having a 4 year degree implies being a good coder. I know examples of both that could not code "Hello World" if their life depended upon it. I also know examples of both that exceed my own abilities. Usually, when the business owners I know think of a "good coder" they do not care about whether someone can implement a linked list, knows <insert language here>, can use version control, or actually documents their code. They want someone who will take their vague picture of what they need and turn it into a working product. For some, a 4 year degree will go a long way, and for others it is just a distraction. Mileage may vary; objects in mirror are closer than they appear (beware of T-Rex).