It's funny that everyone treats Bowser like Sakurai forgets he exists, but you have to remember that on launch he was significantly better than in previous games. If Brawl!Bowser was what we got for Smash4, then we'd be screwed, but we aren't. Infact, a lot of people complained that Bowser felt OP on launch, and still occasionally do, so I get the feeling that not buffing Bowser is more down to keeping the game fun for newbies, whereas not nerfing Sheik and ZSS, etc is to basically not piss off fans of those characters and keep the competitive scene happy that they don't have to suddenly throw down their main because it got nerfed to dust (Even though *cough* DIDDY HAPPENED *cough*.).
I personally just don't think heavies live up to their name enough. Because of combos etc. they're cripplingly easy to damage and in turn, KO. So it just makes you think they need a super-armor-esque mechanic for these characters that isn't as weak as, say, Bowser's "Tough Guy" (Which is basically "Don't flinch at 1% damage attacks if you're not already damaged.).
In regards to U-throw, I don't think it's really that horrible an addition. It's fine to complain about Bowsers on FG picking it up and spamming it, but it's only ever going to be as annoying as, say, Ness in general. -and a lot of people have already found ways around bad Ness players, so bad Bowser players aren't even really a problem. IMO this is actually a good, fair buff, and I don't think they can rightfully nerf Bowser for it (I mean, the first guy that actually even tried to abuse this on me (In a salty ditto, no less.) whiffed, so it's not like it's totally skill-less. (You tend to have to read DI, too, etc.)).
I just think they're listening a bit too hard to the community in terms of what makes a character good. You'll notice that on release Bowser was improved through his mobility, and now we're getting a combo throw it all feels like a very uniform buff you could apply to any character, and beside the point of heavy characters. I'm pretty sure similar things happened to all the heavies actually, most notably Ike who got huge mobility buffs in whatever patch it was (-and IIRC throw options) and is now semi-respectable as a character.
While I think it's the wrong way to buff these characters, since it's not playing to their strengths and attributes it's still a fair buff, and it's just ridiculous to complain either way (Even if I do think post-buff Ike can go eat a ****.).