Is there a large amount of people leaving because of the patch?
In my little world, I lost one friend from burn-out (tried to get him to donate his riches to me no dice ) but had 5 new friends join up.
I'm still having fun with this game, glad I'm not focusing on the end-game/grind/farming part.
D3 leveling from 1 - 60 isn't bad imo assuming someone doesn't go wtf over the difficulty levels and replaying content (which basically means a game like Diablo isn't for them)
the problem is as you said once you hit 60 and trying to farm or progress through Inferno
patch 1.0.3 made a lot of people's builds and gear itemizing no longer or less viable, so they either had to reitemize and/or change build. many chose instead to quit D3.
I chose to make a new character. I quit playing my WD and started leveling a DH because the build & gear I used with my WD was fun for me to play pre-1.0.3 but that fun was gone post-1.0.3 and I did not want to reitemize and play a different build with my WD.
other issues that 1.0.3 produced is that the repair cost makes gold accumulation grow at a lesser rate and since the most common method to upgrade gear is to actually build up gold wealth rather than self farm item upgrades, it makes playing more discouraging and grindy
Blizzard also added higher iLvls to be able to drop in A1/A2, but also nerfed higher iLvl drops in A3/A4. the players that have been farming A3/A4 noticed this change which makes the item farm for them more grindy.
so while Blizzard nerfed Inferno monster damage to lower the quality of tank gear stats needed for Inferno, they added a lot of things that makes D3 less fun and more grindy.
the new enrage mechanics for bosses also really screw HC players.