Not necessarily, Bernie. Countless professional brewers use the same yeast strain for a dozen if not more styles in their breweries, and the flavor profile is just fine.
For years, in the beginning of the microbrewery Renaissance, Alan Pugsley acted like a Johnny Appleseed. He went all over the country selling breweries and training brewers to use them. He got all his training and equipment from the Ringwood Brewery in UK. Thus, many breweries continue to use Ringwood as the "house" strain to this day.
In my last full-time pro brewing gig, I used three strains: One generic ale (White Labs Cal V), one Belgian (Forbidden Fruit) and one lager (WLP820). I brewed at least two dozen different styles, from Oatmeal Stout to 80 Shilling to IPA to Old Ale with the Cal V, at least four Belgian styles with the Fruit, and three lagers with the 820.
So yeah, you can use a different strain for each style you brew. But it's not
necessary. Hell, sometimes it's just plain dumb, like using "Irish Ale" for Dry Irish Stout.
I don't mind having three or four yeasts exclusively. It means I know their characteristics inside and out. I know how they taste, I know their fermentation characteristics under a variety of environmental conditions,
I know how they operate. That means I can practice excellent yeast management at home, just like I used to do when the fermenters were exponentially larger. "Know your yeast", that's my motto.
You don't
need to use a different strain for each style. You don't
need to use a Scottish ale yeast for Scottish ale. Any clean-fermenting, low ester yeast can make excellent Scottish ales. Hell, I've brewed excellent, true-to-style Scottish ales with Ringwood, fer crissake. I'll admit you need a different yeast for Belgian styles and lagers, and it helps to have both estery and clean basic ale yeasts. But you
need nothing more.
So I have four yeasts. One relatively underattenuative, fruity English strain (S-04), one relatively dry, neutral strain (S-05), one Belgian strain (Ardennes) and one lager (34/70). Notice 75% of the varieties is dry. I think I do just fine, thanks.
Okay, I tell a lie. Once a year or so I'll do a Hefeweizen.
Cheers,
Bob