First, I didn't say 100W speaker, I said 400W speaker and 50W amp. Second, if the tweeter is weak, it is usually blown just by increasing the total volume level and the corresponding increase in the high frequency component. Doesn't have to do anything with clipping. Sure, clipping will give some extra power due to distortion, but the tweeter will be blown by the high level non-distorted part just due to the high volume.