I have worn a pebble steel before and I didnt like watches before the pebble and I hated big watches.
I would say people who like the 38mm have not worn watches before the apple watch for a long time.
Here an other photo. On this the 42mm look enormus on me. But it doesnt as you can see on my other pictures.
Next to it a Samsung Galaxy Gear. Just for showing how small the 42mm is compared to other smartwatches.
Image
I guess some people like the oversized look? That Gear is huge.