[jschulenklopper]

And having a better view on the competition in the neighboring lanes (just like in track running). There's even some applied psychology here, that competing swimmers 'push' each other to higher speeds because they can see each other more clearly (and 'feel' the push from someone just lagging).

Putting the faster qualifiers in the middle lanes is also a better view for the spectators on both sides of the pool.

[iknowSFR]

Interesting to see the 400m and 200m track and field athletes starting to favor outside lanes.

[rurban]

That's because of the drag in the inner curves. There the outer lanes are faster.