You have to understand that one of the big debates within the protestant community is between Calvinist and Armenians (sp). Calvinist believe you will only come to repentance it so moved by the Holy Spirit of God, through that perspective what he is saying is that when you have blasphemed the holy spirit you will *not* be moved *ever* to repentance and that if you are truly moved that way you have not committed such an offense.
Armenians (example: Nazarenes, Weslians) believe man chooses to serve God and through his choice, and Gods grace, he is redeemed by the Blood of Christ. Calvinist believe God has chosen the elect and will preserve them until such a time as *his spirit alone* draws them near (i.e. we have no say in the matter, its *only* Gods grace).
I see. That debate would certainly be reflected in the debate about what the unforgiveable sin is.