It is an important point that needs addressing. Since the 5 team group format kicked in in 2003, the "smaller" countries have been having to cope with this.
In future, it is going to cause more problems than it has already done. While rugby is not the closed shop that cricket is, it can still seem like an Old Boys Club who've drafted Argentina and Italy in to give everyone else hope.
Professionalism will see teams joining the top table. Argentina have already done so quite emphatically and Italy have got to a slightly lesser level. Georgia and Japan stand out as obvious candidates to be the next nations to step up to the plate. (In fact, Georgia vs Scotland suggested that they're not far off at all!)
The Rugby World Cup should have a theoretically equal chance for its 20 participants. The best way to do this is to (as football does) assign match dates before the draw to "positions" in each group and thus draw teams randomly into those positions. The times of the matches can still be adjusted to meet TV needs afterwards (a problem that if FIFA needed to address, at least doesn't).
For the 2015 World Cup, this would mean New Zealand, Australia, Japan and the Pacific Islanders getting "first refusal" on night games (so they'd be on in the morning in the East) with the Americas teams not kicking off before (say) 3pm. This is eminently do-able, and really, to be fair to its upcoming nations, should be implemented by the IRB.