I agree. Not everyone is able to do both physical and mental labour to the highest standards (I admire those who can!) Both types of work are essential for life, and progress doesn't only come from mental work (i.e. some ideas need people to construct and manufacture things so they can come to life).
Personally I prefer mental work. I can work like that for weeks on end, without seeing anyone and only stopping for food, washing and the occasional internet to relax in the evening. I've done it. When it comes to physical labour, forget it. I helped some builders out once, and couldn't believe the effort needed. Exhausting. Other people get exhausted just thinking about mental labour and academia.
I actually think this devaluation of physical labour is very obvious in the UK. Until the recession hit in recent months, everybody was encouraged to go to university, regardless of if you were academically able or not (you can get 3 Es at A-level and still go to uni.) University is expensive, and especially with the economy as it is now there are fewer jobs going for graduates. Most people who have graduated, no matter what their results, subject or their university, are looking for the admin and graduate jobs rather than skilled practical labour.
Meanwhile, many British people are on job-seekers' allowance because they see physical labour as being beneath them. This attitude has been encouraged by scrupulous employers for a few years now; they've been taking on desperate immigrants and paying them minimum wage or lower for longer hours. Obviously this makes the British who were doing these jobs beforehand very upset that they're now competing for a lower wage than they had before, and automatically devalues this kind of work.
I sense that things are going to change with the recession, as people appreciate productive work again (like manufacturing and trades) because it is what keeps an economy going, at the end of the day, not services jobs. Plus there are fewer services/graduate jobs going, so people need to re-evaluate their careers.