If you can't see both Uni parks in one day, you're not trying hard enough. I could easily take 2-3 days at Uni, but if need be, I can absolutely hit the highlights in one day, and if I'm feelin' like a high roller, purchasing Express would let me hit all the rides more than once.
Park hopper tickets are NOT a rip-off, not at Uni, and not at DLR. Some people don't want/need to see every ride in both parks - some people have favorites in each, and only a day to spend. Now a one day park hopper at WDW - that's a rip-off. Lose an hour, sometimes two moving between parks - can kill your day, especially for someone with limited time.
Uni found a way to incentivize park hopping. It's not a rip-off if people WANT it, and people WANT to see all the Harry Potter attractions in both parks. Uni's Potter strategy is unbelievably brilliant. You can bet your if Disney found a way to incentivize a ticket upsell they'd do it.
What's hilarious is that they think they have. MagicBands, only $12.95 on top of your $99 1 day ticket! And what does it get you? Um, well...uh...the convenience of having a wristband! And you can pay more to stick rubber character faces on it! It's AMAZING!
At least Uni's upsell incentive is an honest-to-God attraction, not some useless tan-line causing dongle.
EDIT: Plus, the two-park Potter experience supports the story. It puts distance between Hogwarts and London, just like in the movies. It's so insanely brilliant. It's the kind of thing I believe Walt would have championed - a premium immersive experience delivered just like the story demands. It tells a story in a way that NFL could never hope to, and never aspired to - it's a whole new level.
