Tuesday’s news of a joint venture between Molson Coors and SABMiller—the combining of their U.S. units to form a single entity that will be called MillerCoors—didn’t come as a shock. Something that big doesn’t happen without a lot of noise preceding it, and market-analyst chatter certainly did. But it’s surprising that it took this long. It’s also questionable whether the deal will work.

The melding of the two companies is a move that’s necessary for their survival. The U.S. beer market is a rich one, but Anheuser-Busch’s dominant 48 percent share of that market has shaped the paths of the significantly smaller Miller and Coors businesses: Instead of acting, they’ve been reacting. The joint venture puts MillerCoors at about a 28 percent market share and will save the two firms the effort and cost of competing with each other.

The new company’s portfolio is bigger and broader, making it better suited to a wider variety of markets. Besides its light and premium brands, Miller brings the craftlike Leinenkugel beers as well as solid imports such as Pilsner Urquell and Peroni, while Coors contributes its surging Blue Moon specialty brand. The firms’ geographical strengths mesh nicely, without much overlap; Coors is popular in the West and Northeast, while Miller does well in the middle of the U.S.

Investors have already reacted favorably to the news, probably because annual savings are expected to total $500 million by the end of the third year. That projection is based on reduced supply costs from economies of scale, reduced shipping expenses, and reductions in advertising and marketing costs.

Again, not startling: Two large companies form a joint venture to better compete with a larger company, rosy predictions are made, and cost savings are projected. Investors are happy.

There will certainly be less money spent on shipping and probably some savings as redundant jobs are cut. But steep price increases are projected in materials, which could eat up savings from reduced supply costs. And the consolidation of wholesalers won’t mean huge savings, as many areas have already consolidated the Coors and Miller houses.

I’m also skeptical about the prospects for saving significant money on marketing competing products like Coors Light and Miller Lite just because they’re suddenly being pushed by the same company, especially when there are at least five other light beers in the portfolio. We saw some marketing that looked a lot like turf wars between Michelob Ultra and Bud Light a couple years of ago, over “low carb” claims; expecting Miller Lite and Coors Light to play nice seems to be a reach.

Which brings up the question of differing corporate backgrounds. Rather than two separate entities simply being jammed together, this is a situation in which each company is itself the product of two different and recently melded corporate cultures—it’s Molson Coors and SABMiller. One potential trouble spot: Coors’ Blue Moon group has to be wondering about a recent statement by SABMiller C.E.O. and MillerCoors vice-chair Graham McKay to the effect that the craft-beer resurgence will inevitably fade.

There’s bound to be a period of confusion and turbulence, an opportunity for Anheuser-Busch noted by chairman August Busch IV in a memo (published on the Web by BrewBlog, (a Miller outlet) that read, “There will be significant transition confusion from this change, and it’s up to us to capitalize on this disruption now.”

Bad news for MillerCoors, since the confusion will probably increase the chances of a merger between Anheuser-Busch and the world’s largest brewer, the Belgium-based InBev. Anheuser-Busch already imports InBev’s products, which might be a “getting to know you” phase prior to a possible merger. A new company—InABuddaDaVida?—would be a beautiful match of overseas and American markets, with very little overlap.

It would also, of course, be much, much larger than MillerCoors, which would have nowhere to go for more U.S. market share—except maybe to Corona, the substantial import player brewed by Mexico’s Grupo Modelo. Too bad Grupo is already 50 percent owned by Anheuser-Busch.

The new deal looks less like a brilliant move than a matter of making a virtue of necessity: a shotgun wedding, not a happy marriage. If chairman Pete Coors can manage to grow both Miller Lite and Coors Light, he’ll have succeeded beyond reasonable expectations.