this is indeed a good remark...
many top exercise physiologists and coaches now advocate a reverse pyramid. Where the approach is the following:
1. you initially work on endurance, Vo2max, and anaerobic capacity without any particular emphasis on lots of miles. Key is that the slow miles should be slow, and the fast stuff should be pretty fast.
Example of Vo2max session:
swim: 8x50m in 35'' on 1' - 400m free - 8x50m in 35'' on 1' (R = about effort time, pace around 400m pace)
Bike: build from 6 to 10 times 1km effort R:1'30'' or 500m uphill
Run: 2x(10x200m @ Vo2max R:100m jog)

Examples of anaerobic capacity sessions
swim: 3x(5x25m spring -not flat out though, avoid building a mental bareer) full recovery, and easy aerobic set between each set of 5
bike: 3x(5x250m ) full recovery easy 4-5km between sets of 5
run: same idea over 150m or so.

Aerobic sessions should be done VERY easy. Definitely below 2mmol lactate.
Example: Luc van Lierde does this period around 7' to 7'15''/mile for aerobic sessions...for someone running 6'/mile off the bike in an IM, that's very easy.

Then, when you get to the pre competition and competition phase, the training will become more specific...effort at lactate threshold, then tempo, then race pace specific sessions (essentially, the range of speed uses converges towards that race pace).

I agree, that this approach has been used by runners for a long time: work Vo2max, then LT, then tempo, then race pace specific....
the endurance stuff should be there throughout the year, but far from an event, there is no real need to put big miles (except if you want it, but once again the pace has to be slow...)