It's only a "very big problem" to a very few amount of people. No reason for Bethesda to change a mechanic in the game for such a small population of people.
That's just business.
Remember when this discussion was about dragons ? I do and look what the end result was... dragons that will never land unless forced to, all they do is circle over head.
I remember when the game first cme out that dragons would land at any given moment just to chomp at you, then people started to complain that dragons where too hard and that they couldn't defend towns properly which ended up killing a lot of NPC's in their game.
I was one of the few that actually enjoyed the fact that the second you saw a dragon you stopped what you where doing to destroy this dragon before it could cause too much damage. And now I look apon the vampire attacks the same way, they just add spice to the game, your always in a constent state of high alert and always on guard. This adds a certain element of ergency to the game, which points you in the direction of completeing the main Dawnguard quest before thing get out of hand.Before you accuse me of calling you all sissies hear me out.
I was in Solitude the second day( in game ) of starting Dawnguard, as I was passing by the little cart market on the way home( it was about 8pm ) I noticed a gentelman derssed in black hooded robes, thought nothing of it just a priest or mage. As we crossed paths I noticed that the finger tips of his gloves where tipped with steel, then I noticed that the steel was sharpened so I look up to his face and saw that this " traveler " was in fact a master vampire. The second our eyes meet he went into DESTROY mode and begain to attack me and the towns folk, the fight lasted a minute or two and the only death was that of the old drunk who hangs out in front of the Winking skever. From this point on I learned a very good lesson, I will make a lap around the entire city, any city , every time I walk in just to make sure there are no vampires.
Once I finished the Dawnguard mian quest the vampire attacks happen less and less and now it's to the point where I only see vampires of any sort out in the wild. So I say that these vampire attacks on towns is just a mechanic of the game to heard you in the direction of finishing the main quest so as to stop the attacks. I really never needed to enter a town while I did the Dawnguard quest and there for never really have that many attacks but they did stop once I had the quest finished.
So if you guys get what you want, a fix to the vampire attacks, you take a event away from someone like me who likes this feature and thinks it adds to the game. And once it's fixed it will be nerfed like they did the dragons and then there will be complaining that the vampires are not as hard as they should be.
So instead of going about your normal business while you play Dawnguard, why not focus on the task at hand and destroy the vampire threat. That way you complete the Dawnguard quest and stop the vampire attacks on towns, just like the main vanilla quest there are points where the dragons are very apparent in the game and then when you finish the quest they slacken. Which is what happens with the vampires, they get worse as you play through but then ease off after you finish the quest.