I live on a "main drag" for cyclists in my locale, so I see a lot of bikes. The commuters are riding pretty much anything with wheels: Hybrids, mountain bikes, drop bar bikes, single speeds, and the occasional "commuter" bike. Some riders are obviously into cycling and/or tinkering, and are riding fancy, historic, or oddball bikes. Every time I think a particular kind of bike is inappropriate for commuting, a commuter passes me on such a bike.
If somebody is thinking of getting started with commuting, and already has a comfortable bike that isn't a theft magnet, I usually suggest riding it to get a feel of their route: Distance, traffic, terrain, weather, payload, parking, and so forth. Talk to other people about their bikes, what they like and don't like, etc. Get used to routine maintenance such as fixing a flat. These things will give you a better idea of your own preferences when you decide to spring for a new bike.
My bike is kind of the US version of the English classic, but thrown together from parts. I'm showing it, just to emphasize that the requirements for commuting can be pretty modest, at 8 miles round trip over relatively flat terrain. On the other hand, this bike is supremely comfortable for me. I had just gotten home from Home Depot with a quarter sheet of plywood:
Also, this is what an IGH is:
