A lot of cats have the tabby gene since it is dominant, the problem is, it's just harder to see the tabby markings come through in black cats since they're so much darker. Sometimes you can see the tabby markings if you look close enough just like you see there! Very pretty!
Very cool! My chocolate brown & white foster cat has ghost tabby markings, but they're so subtle I doubt they'd show up in a photo. You don't even really see the stripes unless you're looking for them, and they're only visible in a few spots, like on the back of her neck.
That's normal. Some cats often have stripes or swirls that are very close in color that you'd need bright light like the sun to see it's different. Tuffy the youngest kitten has dark brown and very dark brown stripes. Gateway and Tux both however seems to be solid black. Socks is a calico and looks like her fur went through a blender. The feral cats outside all are plain stripped except for the mostly white cat.
Newt has them as well (she's mostly black), but her tabby stripes are only noticeable when she's sunbathing on a bright day, or if you use a strong flash at certain angles when taking a photo of her. I suspect her kitten Newton has them too, but his coat is much darker (and thicker), that it's just about impossible to tell.