The Kingdom of God and the Kingdom of Heaven: The Same or Different?

I have been researching the phrases "Kingdom of Heaven" and "Kingdom of God," and whether there is a difference between the two.  Kingdom of Heaven is used throughout the gospel of Matthew, while the other gospels use Kingdom of God. 

Some scholars believe that both phrases mean the same thing.  In his book, New Light on the Difficult Words of Jesus, David Biven states that Jesus often used euphemisms for God (including the Kingdom of Heaven).  His audiences would have been shocked if He had not because it was forbidden for the Jews to utter the name of God.

This thinking seems to fall apart, however, when you look at several other passages in the gospel of Matthew.

Matthew 6:33:

But seek ye first the kingdom of God, and his righteousness; and all these things shall be added unto you.

Matthew 12:28:

But if I cast out devils by the Spirit of God, then the kingdom of God is come unto you.

Matthew 19:24:

And again I say unto you, It is easier for a camel to go through the eye of a needle, than for a rich man to enter into the kingdom of God.

Matthew 21:31:

Whether of them twain did the will of his father? They say unto him, The first. Jesus saith unto them, Verily I say unto you, That the publicans and the harlots go into the kingdom of God before you.

Matthew 21:43:

Therefore say I unto you, The kingdom of God shall be taken from you, and given to a nation bringing forth the fruits thereof.

In Matthew 12:28, 21:31, and 21:43, Scripture tells us that Jesus is addressing the Pharisees (also referred to as chief priests) or the elders.  If Biven is correct, why would Jesus use the phrase Kingdom of God when addressing these Jewish leaders?  What confounds me even further is that in the other gospels, there are several passages—which are obvious references to similar passages in Matthew—where the phrase Kingdom of Heaven has been replaced with the phrase Kingdom of God.

As much as it would be very tidy to say that the two phrases mean the same thing, the fact that Jesus uses both terms in Matthew has me wondering if they must mean something different?

Clarence Larkin writes that the Kingdom of God represents the reign of God over all things in the universe and is spiritual.  He also states that the Kingdom of Heaven is of “time and sphere.”  The time is between the first and second coming of Christ, and the sphere represents all of Christendom.

Scofield (according to David Reagan) takes the view that the Kingdom of Heaven “signifies the Messianic earth rule of Jesus Christ, the Son of David.”  Reagan concludes that "the kingdom of God is the kingdom set up by God. The kingdom of heaven is the kingdom that finds its source in heaven." Others say that the Kingdom of Heaven is a political kingdom. 

There are other explanations offered by other authors, but none of them completely satisfies me.  What I do know with absolute certainly is that every jot and tittle in Scripture has been placed there for a specific reason.  I may not see it yet, but pray that one day the Lord will reveal it to me.