When your logo is 'A large triangle with two triangles 1/3rd the size of the larger one cut out' chances are that you will run in to others that have done the same thing, only slightly different.
more to the point, why would you change a logo where brand recognition is part of the product! (i.e. I know customers on my site will recognise this icon as a trusted mark that it is secure)
Most people want to believe their brand is as special as Coke or Apple, but they usually aren't. Most people will not know what a Verisign logo on a web site means in terms of actual security measures, they'll only see it as a label saying "hey we claim to be secure!" And those who are familiar with Verisign will associate the logo with their misdeeds, and wonder why they should do business with a site that does business with such a company.
