What a load of mathematical bollox.
You forget to take into account something called difficulty........ the network compensates for hashing power.... as it scales up so does difficulty.
Now.... What might work.. is that you buy a load of ASICS then you dos the network taking out your competitors.
How do you DOS the network using ASICS? By mining blocks with 0 or 1 transaction in them? If so... how does that harm your "competition"? Competition in what? You make no sense to me, neither mathematically nor otherwise.
Just to play "devil's advocate" -- let's just imagine a world wherein a group of hackers (let's just call them anonymous) were to launch a DDOS on a number of larger pools (and also smaller ones, doing as much damage as they can) AT THE SAME TIME that some "anonymous" individual or group of individuals begins to mine with ASIC's 'en masse'
let's also assume that they were to do this as close as possible to the next difficulty change... how long could they keep this up? how long before the difficulty would react? how much profit potential would such a scenario present?
**edit** sorry, forgot to answer the question "How do you DOS the network using ASICS?" :: answer, you don't. you DoS the system using conventional means. The ASIC's would be used solely for mining the most coins possible during the disruption. (*I don't believe anyone interested in profiting would attempt a 51% attack btw*)