Recently, european governments have agreed to revisit the ban on Modi and started engaging him in business deals. All the european governments have started endorsing Modi's vision.
US has still not revisited their earlier decision of non-engagement with Modi. If Modi becomes PM (whch is more likely to happen in 2014), then US will relax the visa norms stating that he has been cleared of all cases by indian courts
Real reason behind all these things are business. Modi as PM will hold absolute power and for Europe and US business people, investment in India will be more attractive and for this they require support of Modi
It is all money at the end. For once, i want Modi to reject the US visa and say that he did not want visa from US. Not sure, whether this will happen, given our mindset of accepting anything from US and Europe