the Word of God is so weak that it suffers to be despised and rejected by people...This weak Word, which suffers contradiction by sinners, is the only strong, merciful Word, that can make sinners repent from the bottom of their hearts. The Word's power is veiled in weakness. If the Word came in full unveiled power, that would be the final judgment day.
(p.173, Deitrich Bonhoeffer, Discipleship)
It would be an interesting question to ask Rob Bell, whether it makes any difference that post-mortum repentance would be in response to the glorified and strong Word of Christ.
I think that when Paul says that he preached "the word of the cross" (1 Cor 1:18), he wasn't just referring to the content, but the form of Gospel he preached. It was weak and foolish, carried by jars of clay, just as Jesus seemed to so many in first century Judea.
At his second coming the Word will be much more a "word of the resurrection", and will be carried by angels blasting trumpets. Glory will be unveiled and strength exerted.
If Rob Bell sees people repenting, and trusting, in response to that Word then is there something quantitatively different to our repentance and faith?