The reason for the slight difference in dating is the imbalance in the population in Russia; due to sheer lack of men it is simply harder to find a husband for Russian brides or Russian women.
In some cases in Russia one can find a woman much younger partner for dating but remember, the greater your age difference, the less the chances of your marriage surviving and more chances of getting married to someone who has no feelings for you, but plenty of financial plans...
Most Bulgarian women on Sesile do look for a husband, but probably 30% seek just chat online and pen pals of their own age from another country and are less likely to be willing to leave their country and settle abroad.
A much larger percentage of Bulgarian women are financially independent compared to their Russian counterparts and are not driven by financially desperate conditions to search for a husband and marriage abroad.
The Russian Mafia runs the cities and bribery and corruption are abundant.
Airline tickets are also more expensive because of the greater distance to travel for meeting the Russian lady of your choice.
This does not mean that you can just walk into a Russian marriage - the Russian women are choosy when it comes to men.
If you are looking for a Russian wife, a Russian lady to marry, or a so called "mail order bride" then you will find that most of the Russian women are on this site for that purpose only.
Bulgarian girls usually have computers at home and will reply your messages faster and tend to invite you to video chat on Skype, while the Russian females will take longer to answer and are interested in a more formal correspondence by letters.
Once you have met with your Bulgarian bride or perhaps Russian bride and you find out that you cannot live without each other you will consider taking her home with you.
For the Bulgarian ladies this is much easier as they can move unrestricted around Europe and more and more visit visas for the USA are being granted to Bulgarians (we have heard that some 50% of the people who apply do get them).
Just keep in mind that their motivation for this may not be as pure as you think and you may find yourself wifeless once she has got citizenship/money through marrying you.