No, commas are NOT optional. Just because someone has not used because they don't know doesn't mean you are free not to use them if you choose not to (of course, you are free to choose not to use them, but that's grammatically incorrect).
If you are addressing someone, depending where you use their names, you put a comma before or after their name, sometimes before AND after their name. Consider the following:
1. John, let's go fishing, it'll be fun.
2. Let's go fishing, it'll be fun, John.
3. Let's go fishing, John, it'll be fun.
So, the rule is:
- if you are starting a sentence addressing someone, you put a comma AFTER their name
- if you are ending a sentence addressing someone, you put a comma BEFORE their name
- if you are addressing someone mid-sentence, you put a comma BEFORE AND AFTER their name
The same goes for hi/hello saluations (they are not exempted because they consiste of only one word; they are still addresses):
1. Hi, John. How are you?
2. John, hi. How are you?