I think that is a load of bs. Manual labor and school are very different types of work, but both are work. I feel like some people (like you), seem to look at kids in college as being lazy because they aren't working on a farm or would absolutely dread having to do that. It is true that most people from the cities that tend to be more studious would hate having to do manual labor, but the reverse is also true. Farm boys from the mid west would fucking die if they had to work and study as hard as many of the city boys do.
I always hear people saying that each and every generation is getting more lazy than the last. In reality i just think the type of work that we are doing in this country is changing as technological advancements are made, and people aren't getting lazier, they're just doing DIFFERENT work. The work is different. Not easier, just different.
On a side note, i think the argument could be made that college students now-a-days are working harder than ever. We are basically required to get a masters or phd if we want a decent paying job whereas our parents only needed a bachelors degree. Also, getting into a lot of undergrad and grad programs is getting more and more difficult.
Oh and i have no bias in this argument, seriously. I was more or less a "farm" boy through high school and then turned into a nerdy school boy in college. I have lived both lives. Neither was more difficult for me, just different