In a textual note for Psalm 45:6, The Expositor's Bible Commentary-Psalms (Tremper Longman III & David E. Garland, general editors, pp. 399-400) says:
This verse is the most problematic of the psalm. The combination kis'a ka lohim [It is hard for me to reproduce accurately the Hebrew - Bobcat], "your throne, God") may be interpreted in a variet of ways:
- "your throne, O God" (KJV, NIV)
- "your throne is like God's throne" (NEB)
- "your throne, O divine king" (Weiser, 360)
- "your throne is a throne of God" (RSV text note; cf. 1 Ch 29:23; see A. A. Anderson, 1:349-50; for a defence of the vocative, see Murray J. Harris, "The Translation of Elohim in Psalm 45:7-8," TynBul 35 [1984]: 65-89)
Longman himself translates it as:
Your throne, O God, will last forever and ever;
a scepter of justice will be the scepter of your kingdom.
You love righteousness and hate wickedness;
therefore God, your God, has set you above your companions
by anointing you with the oil of joy
Arguing against saying that the king addressed is God Almighty himself is the fact that the Psalm was originally about a Davidic king and it is not likely that the Jewish writer of the psalm would mean to express that idea. Also in the context the king himself is referred to as having his own God ("your God") in verse 7.
On the reverse side of the coin, I think people in ancient times would have less problem giving a son of a royal family the same honors that they gave his father. The whole argument about whether Jesus should be worshipped or not (in connection with the WT) seems more to be, 'Are you on our side or theirs? Are you Democrat or Republican?' With little willingness to accept that there might be some middle ground.