It was an exercise in quirky branding on my part - http://bvckup.tumblr.com/post/3283335299/how-bvckup-got-its-.... To my excuse it was almost 5 years ago, long before using "V" in place of a vowel became mainstream. And, in retrospect, I should've picked something a bit more pronounceable.

In Svpply and Svbtle it simply stands for "u", which is a deferral to how Romans would've written it.