Though vampires excel at blending in, they still are outsiders to society in general. They are somewhat reclusive, seeking not to attract too much attention. They never seek or stay in the limelight because that would risk discovery of what they truly are. Not only do most vampires have a reclusive personality, but they locate themselves on the periphery. Whether this is a villa or mansion on the outskirts of a city or an exclusive penthouse apartment, the vampire remains apart in order to protect her identity.
This behavior is likely influenced by the Victorian mindset, which favored wealthy recluses with eccentric behavior. This could be traced back further, to the post-Reformation period rife with its witch hunts where outsiders and recluses were often targeted by the trials. While the Reformation sought to punish outsiders, the Victorians regarded their reclusiveness as eccentric, possibly even desirable given the often deplorable conditions within the cities.
The reclusiveness adds to the mystery of the vampire, which is also often seen as a desirable trait. They are not seen as being standoffish, but rather as exotic, and so maintain a level of freedom with regards to the standards of society.
Count Dracula was a literal outsider from another country, so his ways were excused by London society; however even if he had been native-born English, his behavior would have been excused by the remote location and the wealth he displayed (wealth excuses nearly all behaviors).
This trait, at first, seems like it would be an easy way to identify a vampire. Yes, they have the ability to pass for human, but the trend of remaining apart from society (both behaviorally and geographically) should stand out as a red flag. Yet there are enough outsiders to society that the vampires simply blend into the background, using their affluence as a shield for their privacy and eccentricities