It isn't designed for any kind of volume. It isn't surprising that it falls over after people hammer the site. What I find funny is that the DDoS they are describing could simply be all their users demanding page refreshes, not some nefarious hacker.
In most cases that's indeed the main cause of an exchange with poor capacity to go down temporarily. I have been (still am) experiencing this with BTC-E from the first day of me using that exchange in early 2013. Till this day they haven't been able (whatever the reason might be) to offer people a properly working platform at peak traffic moments. In case exchanges really suffer from a ddos attack, they mostly throw out a public notification stating exactly that.
Poloniex is already known for having this kind of problem whenever trading activities heats up. Worst it goes up when trading is already over making users lose a huge amount of money. I wonder if it is really the connection problem or an inside job to reap all the profit once coins are hyped.
