Some good points there, Goughy.
I do have to say though, with AM, that it is odd that it is bowlers who get the bum wrap when it comes to cross generational comparisons. Batsmen and fielders are more deserving.
This is most clear with spinners. It is difficult to see how the task of spinning the ball effectively down the pitch is any different now than 75 years ago. Warne and Murali are perhaps the best 2 spinners of all time - but they would be irrespective of whatever time period they were born in. Their abilities are a reflection of their innate skill not out of any great improvement in standards of physical strength etc.
The same applies to fast bowling. A great deal has been made of gym sessions and diet and nutrition and so on and so forth, but from all accounts fast bowlers used to bowl plenty and plenty of overs especially in country cricket. Indeed this was how they got match fit, by endless hours of bowling. Moreover, these individuals often came from backgrounds where physical labour was part and parcel of their daily lives and they often worked too, and were therefore not mollycoddled into 2 hours of training and a nap.
I would therefore say that, as Goughy has stated, it is likely that average speeds have improved due perhaps to the general increase in health and well-being of the human population, but in terms of maximum speeds I think the differences would be negligible. The best fast bowlers then were physically prepossessing specimens as they are now, and they do then what they do now, deliver the same ball down the same length as fast as possible.