Here's when the law of energy can be applied "Energy can neither be created nor destroyed. It can only be converted from one form to another".

=> for beatiful concepts: beautiful stuff can be created but not be destroyed. They can only be changed in form.

=> concepts like blogging can be created but not be destroyed. They can only change from one form to another. (similarly for PDAs)

PDAs aren't dead yet. Are they? They have just got better and are called mobile phones. Its not that mobile phones have their features.