If your team isn't built with the acknowledgment of the most overused pokemon in the game and doesn't have a way of exploiting it in some way, it isn't a good team, case closed.
We (or at least I) urge our competitive battlers to think about Blissey in the same way, and relish the many, MANY opportunities there are to use her presence against those who use and rely upon her.
Quoted just for emphasis. It's always better to play your opponent than to try and cover everything. You're bound to win more if your team is designed to counter another person's team. If Blissey shows up almost half the time and you have a surefire counter then you've got an element of a counter team for about half the teams out there.
EDIT: And all this talk about being able to counter the hard hitting physical attackers so we shouldn't need Blissey to counter hard hitting special attackers is kind of silly. Part of the reason why teams can deal with physical attackers without using a physical defense counterpart to Blissey is because Blissey gives teams the luxury to use a combination of defensive pokemon of different types to abuse resistances and immunities. With Blissey you don't have to worry about special attacks as much and can then focus your team on the physical end. I'm not saying it's impossible to make a team without Blissey or anything but without it the game changes significantly.