Stupidity rules!
1) Wheter the disk is writable or not, a DoS attack means too many connections , too less bandwidth, and/or too slow computer. Ergo: Data is saved, but it doesn't really help prevent other means of irritation.
2) I don't know how they will manage it, but you really need a writable harddisk, if you want
a) log all or some requests.
b) update database requests.
c) have a dynamic site in terms of interaction with the community/users.
So, if those things aren't possible, the site in particular is probably nice watching once, but then will only fail to interest people. Which has as consequence that, indeed, less people will try to hack such a site. Which is in terms of marketing of this harddrive, maybe, a good point. Nobody hacks it, because why bother boring sites.
Ah, what the hell.
