Chemically, molasses and corn syrup are very similar in terms of composition and viscosity.
Molasses would be sucrose; corn syrup would be glucose + fructose. Sucrose is made of one fructose + one glucose, covalently bonded. The viscosity is dependent on the water content.
In the case of the students, the decision to use corn syrup instead of molasses could have been for a number of reasons: the cost, the smell, or the potential of molasses to stain things could all have been factors.
It is not unusual in science to use something that is similar to the substance actually being studied. As long as the proxy is validated to behave like the actual substance in the conditions being studied, the results are completely valid.
We use all kinds of proxies to stand in for human beings in medical research.
Ed
I think a term is needed to denote "experiments" that are merely rehashing of well known / understood behavior, as opposed to research experiments that may break new ground, or at least confirm previously limited / uncertain data.