I was just wondering what the difference is.

Your probably describing three tab shingles that look like bricks, and architectural laminated.

If so ,.....the three tab has expantion joints cut out, those being the slots, and is one layer thick only. Its weakness is that the top of the slots is only two inches to the top of the shingle before its joint headlap. In the slot, it exposes ten inches of the shingle below it, and is only an inch from the nails.

...The architectural shingle uses two laminated pieces to let expantion happen without the cutouts. nails are better protected, they simulate wood shingles, and the only place its weakness exsists is two inches up under the one above it, from where two shingles meet.

Layouts and exposure are different because the aplication methods are different.