That's really good advice, the goal of blending is to get a better wine out of the blending stock.
A lot of Bordeaux houses used to favor Cab alone when they made wine to lay down for 20 years; now it's common to blend in some Merlot to mature the wine faster. Were the older ways better? Depends on what you like and when you want to drink it. There are no hard and fast rules, some still make it that way because that is what they like. That said, what most people refer to as a Bordeaux blend is mostly Cab Sauv, about half as much Merlot and a little Cab Franc.
They also pay attention to the ground, drainage and sun exposure when planting; some of these are blended in the field.
To be honest if you went to 5 different Bordeaux houses they probably do things a bit differently in each one and all are going to be a little different. You might be able to give each one the exact same grapes and chances are none of them would end up identical.
You have to evaluate what you have in front of you; if you can make it better by blending do that. That's why it's an art, if it were a science anyone could make great wine from a recipe.
Joe
