Come on, its about time they started doing this.
Most new games, and MGS2 also, will require a 1gig processor and a decent graphics card and so forth. DVD drives have been on new computers since ~500mhz, and any "casual gamer" has to keep with the times.
How many machines with a high enough spec to run games like this DON'T have a DVD drive??? Besides, they only cost about £25 now, its hardly going to break the bank.