This happens a lot lately, incorrect bundle prices on the Steam Store.
In some cases buying all games seperate will be cheaper than when you buy them in a bundle or gamepack.
Most recent example is the “Company of Heroes” bundle which is on sale as weekend deal this week.

In this case it’s just 2 cents (1,59 + 1,39 + 1,99 = 4,97€ ), but sometimes, rarely but still, the pricing difference is way bigger than 2 cents.
For a company such as Valve / Steam this is just bad advertising caused by themselves.

Anyway, if you want to check out the weekend deal, click here: http://store.steampowered.com/sale/COHWeekendDeal