Right, sound funny, but let's see what's happen after block 50,000 where the block reward down's to 0.5, i don't think it could be a good idea spend 1,000 watts of energy cost to mine a coin, but a 100Watt 6Mh gridseed blade or even a PC could be.
That is only true from block 50,000 - 100,000, and then reward would be 1 for blocks 100,000 - 200,000 and so on. So it will only slow down in the early stages of mining. Block times are so fast I have mined 3000 block in 12 hours.