Commuting can be as complicated or simple as you want it to be. For some people, bike commuting is just a way to get to work, and they don't want to invest any more effort or money than what is absolutely necessary to accomplish that. For others, it's an extension of their cycling hobby, and they enjoy investing in the best equipment and clothes.

Like probably many others, I started out relatively simple and became more complicated with time. I started commuting more frequently, in a wider range of weather conditions, and my route increased in distance. Eventually, the bike that seemed fine riding 20 miles round trip 1-2 days a week seemed inadequate for riding 30+ miles round trip 3-5 days a week. One good thing about cycling gear is that most of it is durable and well made, and it tends to last a long time. So, after your initial investment in a new bike, seat bag, rain jacket, etc., you usually don't have to replace for a long time.