Any seam is subject to stress and can open; I'm no engineer but I wonder if a seam on the side would not be subject to just as much stress. My Solera was built late 2012 and delivered in January, and has the seams on top; I do recall reading when that change was made, but can't recall offhand when it was!
At any rate, an ounce of prevention is worth a pound of cure. I think an application of Eternabond over roof seams is a good idea - from reports I've read, it does a very good job and lasts a LONG time. If the seams are on the side, that would be rather unsightly - but checking regularly, and resealing with clear sealant would be advisable.
And yes, you can walk on the roof without concern. I weigh in at around 220#, and walking on roof seems very firm and secure, but as previous post stated, I wouldnt try jumping up and down.