While I agree with you completely on your explanation, I must point out that the treacle/water analogy is flawed - there is now difference in maximum potential swimming speed.If you are swimming in treacle, there's a good chance that the guy in the next lane from the 8 swimmers BEHIND you will finish before you do as he's swimming through water, and you're in treacle.
The increased resistance from the treacle will be offset exactly by the increased thrust provided by the more viscous medium. However, I suppose the treacle-swimmer would get tired quicker.
Anyway, moving swiftly on...