Pastor Armstrong commented that some other religions believe that there are different levels of rewards in Heaven. Can you explain further?
Since you didn’t reference a specific VBVMI teaching in your question, we don’t know which comment by Pastor Armstrong you were questioning specifically.
In general, while many false religions teach “reward systems” of one kind or another, they differ fundamentally from the Bible’s teaching on eternal rewards. The key differences between Christianity and false religions is in who gains rewards and what the rewards is.
In false religions, the “unsaved” are competing to receive the reward of heaven (or a level of heaven). In their view, greater works results in a better chance at entering heaven or at achieving a better level of heaven, while a failure to do sufficient good works results in loss of salvation and damnation. So these false systems teach that works are a means to salvation.
The Bible teaches that only those who are already assured heaven (i.e., “saved”) can earn rewards, and the reward we earn is not entrance into heaven or a better heaven, but opportunity for greater responsibility serving in Christ’s government with an inheritance (i.e., land) in His kingdom. So in Christianity, only the saved can "compete" for rewards, since the Lord does not offer salvation on the basis of works. Instead, He grants salvation to those who by faith trust in the work of Jesus Christ. Faith alone is our means to heaven. For those who are already saved, works are a means of pleasing the Lord Who has promised rewards for our service.
For a complete teaching on eternal rewards, please read Explaining Talents and Minas.