I wouldn't go so far as to say "frequently", but it's fairly obvious they've become a LOT more international since the acquisition by Beretta, and they adhere to the demands by the market.
Point in case: their .416 Rem Mag. My friend has one, and I was talking with one person in the know not long ago. Both agree that the recoil of the rifle is absolutely horrendous. This mentioned person in the know asked Sako's product development director why they made the rifle so light that it's virtually impossible to shoot. They had conducted a market survey, you see, and the result was the buyers want a light rifle. So be it.
Sako's recent model changes have certainly all been in the direction of appealing to a larger market rather than just the conservative domestic market as it used to be.
Part of the reason for keeping the same action for a long time was also cost of development and lack of money. Sako has always been a small manufacturer owned by a plethora of other Finnish industries over the years, and none probably were very keen to invest heavily but settled for the domestic market. Since the demise of their model 92 assault rifle (i.e. when the Finnish army stopped buying domestic guns) they've focused on the sport guns and initially rather heavily on the domestic/Nordic market. Beretta changed all that.

Whether we'll see the two-lug guns I frankly doubt - but if the market demands it, then they'll make it!
The current 85 is a further development of the 75 and for sure the press agrees that the new action is an improvement over the previous which was not bad. The virtues of it are fairly obvious: low opening angle and smooth operation as is a Sako trademark. Yet it's modern = cheap to manufacture.
To my understanding the biggest difference between the 75 and 85 actions is that the 85 is genuinely controlled feed whereas the 75 was not although so marketed.

BTW, forgot to point out one more thing about Tom's rifle:
The one with the lock is one of the short-lived "Key Concept" models. Sako did introduce it with some fanfare, but many have voted it to be the most unnecessary invention of the shooting world so they buried it quietly.
I'm not entirely sure if the Key Concept was only ever available on the 75 or on previous models also, but I think it was a feature of the 75 alone.

- Lars/Finland