I think the confusion here is perhaps due to comparisons
based on metabolic equivalents (i.e. calories burned)
versus training effect.
Based purely on a calorie expenditure basis, the ratio
for swimming to running is about 1 to 4 (varies a bit depending on swimming speed) as indicated above,
however the ratio for biking is actually even less than
4 to 1. It depends a lot on speed but is typically
around 2.5 to 3 to 1 for a biker averaging 17-20 MPH.
A biker doing a 100 mile bike ride does burn a lot more
calories than a runner does during a 25 mile run (of
course it takes the biker twice as long to do this, and
his calorie expenditure per unit time is less than the
runner's).
All of this says nothing about how to compare the
training effect of the two workouts which is what I
think the poster is really asking about and I don't know
the answer to this question. It is worth noting that
professional triathletes typically spend a hell of a lot
more time on the bike than they do running (most don't
run more than 60 miles a week).