David,
>>>What is the philosophy behind it?
First of all, let me explain what the 'Account type' field is needed for.
Let's presume that your site is a business portal for potential employers and those who is looking for a job.
So, there should be two different sets of profile questions separately for the employers and for those looking for job vacancies on your site. That's why you should create an additional Account type and select the different profile questions for it.
And if while searching you choose a certain Account type, you will see only those profile questions that had been set for this type. And there is no needed to change the 'Account type' field for multiple choices, because if you are an employer you will search only for the people looking for a job.
User Roles feature is a members' limitation. You can set the limit for each of the member roles. For example: You have two roles - 'Standard' and 'Gold'.
A member with the 'Gold' role can read forum topics. But a member with the 'Standard' role can not do it, as his role limitations do not allow him to do that.
You will be able to select the services that will be available for members with 'Standard' or 'Gold' roles.
>>I was wondering if this was normal or what caused it. Was it adjusting account types after the account had been created?
Have you deleted any account types while playing around with them?