As was already pointed out, in a primary race you run toward your primary voters. Who tend to be the most committed. Which usually means they are more extreme in their viewpoints. Either further to the left (for Democrats) or further to the right (for Republicans). Clinton and Obama are still trying to win their party's nomination.
1) A year ago, it was long odds that there was any chance at all of the GOP winning the Presidency in 2008. Considering the two opponents, I think the odds look much better now. I think it is better than 50-50 right now. Obviously McCain could still blow it but these two have problems. Hillary has such deep negatives that she will never be able to get the massive support from the middle she needs. And sooner or later the population is going to realize that Obama is ideologically aligned with George McGovern. And you remember what that election looked like. In my lifetime, there have been two elections where one party or the other picked somebody from the farthest wing of their party. The Democrats with McGovern in 1972. And the Republicans with Goldwater in 1964. Both were wiped out in the general election. It is DARN HARD to win the general election with either super liberal or super conservative. No matter how personally engaging. This is the upside with McCain and his appeal to the middle.
2) If the Democrats do win, I think they will mostly vote around the margins of the issue for the first congressional term. Try to ban .50 rifles or something like that. Flirt with a new AWB but somehow just never quite seem to bring it to a vote in both houses. After 2010, 2012, that might change.
Gregg