I too can't understand the reluctance to update to avast 5.0 unless your OS isn't supported (win9.x, winME) ? Avast 5.0 has been out for almost 9 months now and as has been mentioned support for avast 4,8 is likely to cease at the end of this year, the clock is ticking.
That is why avast are trying to get people to move before support ceases and they have a flood trying to update at the program all in a very short time, which would put a heavy load on the update/download servers.
You are looking at a support forum where you generally only see people with problems, that is the nature of a support forum. However, with over 130 million avast users and the majority of them on avast 5.0 who aren't swamping the forums reporting problems.