Okay, I must say "oops, it just happened to look like that design" is a really lame excuse. (Additionally there are art laws and cease and desist laws can and have been filed amongst the collaring community)
That's like saying there are only so many ways to photograph or film or paint something. Talk about selling ones self short.
Sure, designs will be similar, sure they may draw from one another, but timing plays a part. Having just made my own leather collar from scratch and gone, crap, I need something to draw inspiration from, because I'm drawing a blank, I understand. In the end I copied the Xdog design, Denis copied nothing and his looks like nothing because it is a complete original.
To say a skilled artist is limited by their craft is wrong though, give me a subject and I will give you well over 100 ways to photograph it. Collar designs obviously are not stunted, judging by the variety of custom and standard designs.