The 3g ipad does have GPS..its called A-GPS. Reports are conflicted on whether this is a true chip gps...but one thing is for certain, it uses cell tower triangulation to assist the gps in getting a fix be it faster and more detailed location awareness. Not good when you're out there.
So there is some historical reason for confusion here. Many devices in the past have been described as having GPS when they weren't actually communicating with the GPS satellite systems. And many devices can provide location information without it - for example the original iPhone.
But, as of today, nearly every cell phone and smart phone has a true, satelite based GPS chip, including the current iPhones and iPad 3G. Cell phones have assisted GPS and that's a good thing - assisted GPS is improved GPS.
For a full, detailed, explanation of GPS and AGPS as it's evolved for cell phones read this article.
Inside assisted GPS: helping GPS help you
In summery, details of the satellite based system are somewhat surprising - without some type of assistance any GPS receiver needs 12.5 minutes to assemble the information needed to fully lock its location from a cold start. The GPS satellites are incredibly slow - they send only 50 bits per second. Modern standalone receivers use a variety of methods to improve on this - they cache some data about satelite locations and remember their last location. This helps them lock a position after receiving partial information.
Cell phones have the advantage of a whole additional set of data and they use it - cell towers and wifi networks. In the case of the iPhone and iPad they leverage technology from a company who literally drives trucks around the country mapping the ID's of household wifi routers. Phones with wifi can tap into this and cell towers to get an immediate idea of where they are. They also feed this to the sattelite GPS algorithms to give it a head start while it tries to piece toghether the slow satellite based data.
So what you'll see with an iPhone or iPad 3G in the middle of the ocean is a device that's not exactly designed to be there. I suspect it's algorithms are optimized to leverage wireless data and will be surprised to fine none. The iPad 3G will absolutely lock your location, it will just do it slowly.
EDIT: Corrected to reflect that only iPad 3G's have "real" satellite based GPS.