Longevity with a glued in battery pack of the rMBPs and Apple's history of discontinuing batteries after ~8yrs could be an issue for collectors/users who keep their notebooks longer than average. Also cost wise Apple makes it costly, my old 13" 2010 needed a new battery which was $120 and later on I heard the price was hiked to $150--at the rate of inflation, if a battery replacement cost goes higher it'll be cheaper to replace on your 2nd battery replacement point(6-7yrs).
...in my situation I'm leaning back to an old strategy of new desktop then notebook cycle. Ever since we've hit dual/quad-core processors, buying a new portable isn't as earth shaking as the past.
Are the issues exaggerated or does the notebook run too hot?
Nobody is forcing you to use Flash, if a site uses multiple ads powered by Flash(Daily Fail err Daily Mail) it'll always push CPU/GPU usage higher up than necessary but you can run browser addons to block loading that fluff.
Processors can hit ~95-100C, the aluminum casing will act like a big heatsink to spread that heat away--most unibody MBP/rMBP rarely heat up as bad as the Powerbook G4/early Core Duo non-unibody.
As far as heat output rMBPs are roughly similar to 2012 cMBPs, warm at best and rarely hot unless you're going to play games for 2-3 hours in which the CPU+GPU will go into full throttle.
There is a reason why Apple began calling portables "notebooks" as PCs became toasty to use/run while on a lap--there are countless reports of people getting rashes/burns from PCs back in 2002 and PowerBook G4 by 2004 weren't the coolest(1.33Ghz processor easily hit 70-75C, aluminum casing would hover at ~100-110F near the hinge and upper function keys). On modern unibody MacBook Pros/Retina MacBook Pros you have less "hot spots" than previous designs.
...if you've met anyone who've owned previous Macs, you'll hear rMBP opinion of it being cooler/coolest running Mac.
