I can see a lot of suspensions being for those very reasons. Sadly public lobbies from what I hear are pretty much the same. Thankfully it makes life easier having mute and block features. Life savers right there. I also make sure to report anyone using slurs and hateful speech if I catch it happening in a lobby I am in.
Now I'm curious to know how many accounts they banned.
Most do. It's kinda rare that any users are banned by mistake. It has happened, but usually they ban you after having definite proof of wrongdoing. I used to report a lot of people on Xbox 360 back in the day, so much that Xbox sent a thank you note to me on Xbox live a couple times lol. If you have an offensive name, profile, say anything offensive, it's easy to file a report against someone. And I imagine Xbox has a way to see exactly what a user does on Xbox live and in games.
Like I said in my point above, most bans/suspensions are investigated before they are finalized. It's very rare that anyone banned or suspended, was by accident or mistake. Most bans/suspensions are thoroughly investigated I hear. Some mistakes do happen, but most are legit and warranted from what I hear.
You can fight the case with Xbox when a ban/suspension happens, but for the most part, they never lift them.