Just as we're all different in the way our bodies work, our 'pregnant' charts can all look different too... a few minutes looking through fertility friend's chart gallery confirms that!
Yes, charts that go up and up can be pregnancy charts. And similarly, I've seen charts where the temps barely reach over the covr line, ocassionally dip below and are still pregnancy charts. Some are triphasic (a second temp shift up after implanation), some aren't. SOme have an implantation dip, some don't. Many will dip at about 4/5 dpo, many wont... You get the idea

But you're right in thinking that they are mostly above the coverline.
To put your mind at rest why not take a little browse through the pregnant charts and you'll notice how different they all are