Landscapers are not designers, but frequently assume that role by default. They will not have the same level of knowledge or concern about details that a landscape designer would have. In "everyday" landscaping, it's often the budget that dictates the outcome of details not carefully outlined in plans and specs. If the spacing is not specified in the contract, then having the stones re-spaced will cost additional.

The "standardized" spacing is close enough to comfortably fit the stride of any family member. The larger the stones, the closer they are laid so that you lose any sense of "missing" a step from one stone to the next or overextending you stride. Really, this can only be achieved by laying the stone out first before seating it.

Stepping stones look good spaced apart, but it's been my experience that the closer they are to each other, the better they work for walking. Lower maintenance too. If you have to look down to see where to step, it becomes awkward right away.
Mike

The less space between the stones the more steady the tread. Try to envision everyone who might walk on this path: elderly persons, toddlers, women in heels, running kids, yourself with a big bowl of fruit salad. The smoother it is the better.

Thank you for the feedback. I think they need to be moved closer. Thanks