To be honest when I saw both instances live, I didn't think either of them were penalties. I've just watched them back on the highlights on YouTube and I'm still not convinced they were penalties.
With the Riis one, it just looks like he's tripping up over himself/the defender. I tried watching it at a slower speed and on a larger screen although the video quality isn't great. There isn't a clear point where the defender grabs hold of Riis' shirt. There's a point around the 00:12 mark where the defender might've grabbed a hold of him (I couldn't quite see it clearly) but it's so brief, we'd be extremely lucky to have a penalty for it. If there is a shirt pull there, Riis goes down way too quickly for the ref to be able to notice.
With the Browne one, I think there's a stronger argument than the Riis one but still I'm not convinced. At normal speed, it looked like Browne felt a hand on his back and went down quickly. Slowed down, I could see the defender trying to position himself in front of Browne but I still think Browne went down too early for that contact to have really brought him down. Plus it was only one hand on his back and one hand on the back isn't enough for a penalty, especially with the force the defender was applying. It's hard to tell from the angle in the video how much the defender obstructed Browne to be fair.
I think the problem in both instances is that Riis and Browne were looking for penalties. They went down too quickly and in these situations you need to let things play out for longer for a ref to be able to see it. Even after a review, I don't think there's a strong enough argument for the ref's body to apologise in these instances.