First, let me state that I'm a 4th generation Italian American; I know nothing about Russian customs other than what I learned in a Russian history class (humanities requirement) a few semesters ago. With that said, I could probably shoot an email to the professor who I took the class with if you want more info, but I think my answer will suffice (but please let me know, he is a pretty cool guy).
Anyway, I would presume it has something to do with Russian culture and the importance of honey in that part of the world. I remember when I was a kid (like 2nd grade I think), we read a collection of short, non-fiction stories of a Russian girl and her grandfather, who was a beekeeper. I cannot remember what the name of the book was nor the author nor whether or not the stories took before or during the Soviet era; but I do remember that honey played a really important role in most of the stories.
Of course there is other more concrete evidence other than my childhood reading material. For instance, just take a look at Russian cuisine. They have a mead-like beverage called Medovukha, which is made with honey and yeast. It's apparently a traditional drink at weddings over there. Also, you've got Russian honey cakes and other food based items. Finally, honey is also a good preservative as it's antibacterial, so it was often mixed in with jams back in the day to preserve them.
So I'd be surprised if many of the ex-soviet brewers didn't use honey as an additive to their beer. Especially if the beers you have in mind are bottle conditioned, they would need to add a sweetener of sorts for proper carbonation. I've used honey in two of my home brews and I like it.
Perhaps some substantiating points:
- Baltika Medovoe Light seems to be a popular "first Russian beer" to try. It's a pale lager with natural honey added.
Indeed honey does seem to have played a central role in Russian culture.
Like the Assumption, the three "Saviors" (Spas), August 1, 6, and 16, were associated with the fruits of the earth. The first was called the "Honey" (medovyi) or "Wet Savior" (mokryi Spas), signifying either the gathering of honey or the religious procession and blessing of the waters traditional for this day.
Ivanits, L. "Russian Folk Belief." [http://books.google.com].
According to Russian historian Vasili Kliuchevskii (1841–1911), we must learn about the Russian forest, river and steppe in order to understand the Russian people. [...] "The forest provided the Russian with oak and pine to build his house, it warmed him with aspen and birch, it lit his hut with birchwood splinters, it shod him in birch bast sandals, it gave him plates and dishes, clothed him in hides and furs and fed him honey. The forest was the best shelter from his enemies."
Riordan, J. "Russian Fairy Tales and Their Collectors." [http://books.google.com]
It's notable how closely intertwined honey and their ideals of paradise were, as found by a search for the term "honey" in "The Paradise Myth in Eighteenth-century Russia: Utopian Patterns in Early Secular Russian Literature and Culture" (Baehr, S. L.).
So, though still conjecture, it may be so that Russian culture has had a higher demand for honey notes in their foods and beverages, naturally selecting those tastes.
Frankly, it may simply be the case that there's not an objective ("provable") answer to this question.