A properly adjusted road bike brake will have no problem throwing you right over the handlebars. My bike has a set of cheapo tektros and I have no problem locking them up.

Two things: first, when you squeeze the brakes are you doing so from the hoods or the drops? If you grab from the drops you will have much more leverage and thus more stopping power.

Second, it's a matter of surface area. On a 700x23 the contact patch (area of the tire that is actually touching the ground) is about the size of a dime. This tiny patch of rubber has to stop you vs the comparably much larger surface area of a mountain bike tire that you are used to.

So...you might want to take that bike back to the shop to have the brakes adjusted. It should be a freebie