In the automotive world, the Porsche 911 has gone 51 years with a 6 cylinder boxer engine mounted behind the rear wheels. Purists would argue that it's not air cooled anymore, but the fact that it lasted 50 years with such a screwball arrangement is nothing short of incredible.
Also, the Ford Mustang has been a sporty two door coupe with a V8 since 1964. Clearly Ford got it exactly right if that platform still has a hold on the market even as it's "pony car" competitors disappeared from the market. They're back now, but none of them can boast the 50 years of longevity the Mustang has.
So, that makes it 27 years for the Blizzard as a steel hardtail (the last Blizzard was made in 2012).
Now, I'm sure someone out there is already racing to the comment box to correct me because the Specialized Stumpjumper debuted in 1982. And it's still in Specialized's lineup today, which would make it's run 31 years.
Except that it doesn't count. Yes, there are - I hope you're sitting down - 21 models of Stumpjumpers available in 2014. Everything from the Stumpjumper Expert Carbon World Cup, to the Stumpjumper FSR Expert Carbon Evo 650B. But not one of them are steel hardtails like the original.
Our next contender is from a brand you might not know, but they've been making mountain bikes since 1983 - Jamis. I don't write about them much, mostly because you don't see them around much. But if they've lasted this long, they must know what they're doing.
In 1993, the Jamis Dragon debuted with a Tange Prestige steel frame. Go to their website right now, and you'll see the 2014 Dragon 29, in two models; a Reynolds 853 variant, and one made from Reynolds 520, both of which are steel.
That gives the Dragon a 21 year run as a continuous model, which is very impressive, especially considering that they're a (somewhat) big company still making a steel mountain bike. Also, you can buy it at SportChek.
That leaves just one more bike that I can think of. In 1987, Moots began building their YBB (Why be beat?) model in steel. This frame involved a spring at the seat stay/top tube junction, forming what's known today as the softtail. A design copied by countless manufacturers.
By 1991, Moots had switched to titanium, the material that they're so well known for today. And just like in 1991, you can get one with 26" wheels. By my count, that gives the YBB 25 years of uninterrupted production.
By the way, if you ever come across a Moots, take the time to examine it up close - the welds especially - and it will make you wonder where the trained monkeys that welded your bike came from. Seriously - nothing out there (except for maybe an Independent Fabrications Ti) is welded better than a Moots.