You are correct that a SedoPro code is not necassarily needed, but for a portfolio with only 200 domains or $200 in earnings it is needed. That is the minimum requirements if you also have a SedoPro code. If you choose not to get a code, then you need to have a much larger portfolio (size requirements undisclosed).
From Sedo:
"In order to maintain high standards of traffic quality, SedoPro asks each applicant to obtain an endorsement from an existing SedoPro member. Endorsement Codes can be obtained from any current SedoPro member.
Admission to users who do not have an Endorsement Code is offered only to the very highest quality portfolio owners, following extensive checks by SedoPro staff. This can result in a delay in the processing of your application, and will make it more difficult to gain admission."
So, it is not recommended to apply without a code as you probably will not get in, but yes, you do need a minimum of 200 domains (not guaranteed to get in) or $200 in monthly earnings (guaranteed acceptance, I beleive).