This is stated in the thread by Danial Cai (MVP), and then later confirmed by Rich Dickinson who is an employee at Microsoft later in the thread.
You can read the entire thread here: http://social.microsoft.com/Forums/en-US/crmdevelopment/thread/7441b27b-bbb8-4693-876a-de64263aa137/
So you might not want to use ObjectTypeCode in any future customizations as we don't know for sure that it will even be accessible in future versions of CRM.
Have a nice day!

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