The reason to have two accounts is for security reasons. If you accidentally leaked your key for your 'personal' account, your witness account would not be compromised; if someone was able to hack into your witness server and steal the key to your witness account, your personal account would not be compromised.

Personally, I just use the same for both. Like you said, it is easier for people to know which account to vote for if there is only one account.

You could look at @lukestokes as an example of a witness who splits accounts though to see how he does it, if that is the way you want to do it.