My analysis on this
1. BJP's over confidence led to its loss in 2004 election. After passing with flying colors in state assembly elections, Vajpayee called for early elections. They assumed it was the right time to bring in elections.
2. India was on its way to progress due to reforms, infrastructure including Golden Quadrilateral. But "shining India"- the slogan, is what earned their loss. The rural and urban poor gave a fitting comeuppance to BJP for blowing their own trumpet. Even LK Advani admitted that they lost in 2004 due to overconfidence & wrong slogans.
I know there's more to the story but if BJP's in your face ad campaigns continue then it might prove disastrous for the next elections.
or may be I am being too critical....