Yes - this was confirmed by Maxis with a community wide email announcement on the 11th of April 2013:
To Our Fans,
SimCity will be coming to the Mac on June 11 as a digital release via Origin™. If you have purchased SimCity for PC, either as a physical or a digital copy, you will receive the Mac version as a free digital download on Origin on June 11.
Via Origin, SimCity is cross-platform compatible, so all players will be able to play together across the same servers. You will be able to play both versions with the same Origin account, allowing you to seamlessly continue cities, achievements and leaderboard progress across the PC and Mac.
If you have purchased SimCity for PC, the Mac version has already been added to your Origin account. On your “My Games” page, hover over SimCity and click the info button. You will then see SimCity on Mac in the “Add-ons & Bonuses” section. You will be able to download and play the Mac version on June 11.
Sincerely,
The Maxis Team
The Wikipedia article for SimCity also cites the same source that you linked, stating;
On November 19, 2012, a graphics engineer at Maxis using the name "MaxisSixAM" commented on the SimCity.com forum confirming that while a purchase of SimCity through the Origin platform will entitle access to a Mac version of the game, there was currently no indication of a Mac release date and that Mac users may be unable to play the game until a later date.
The post on the EA forum that you linked (which seems to have died) did seem to indicate that this is the case, more specifically, that if you purchase the game via Origin, you will be entitled to play the game on either platform once the Mac version is released.
The EA platform Origin does state that licenses for games available on both platforms will be transferable, though doesn't explicitly mention SimCity.
One new feature will be of particular interest for gamers who play on both PC and Mac machines: dual-platform play. For select EA games (that are available on both PC and Mac), you can buy a title once on Origin, and when you log into Origin on either Mac or PC, that same game will appear in your newly unified (Mac/PC) My Games library.
This will likely work in the same manner as Steam, in that once you own a license key for the game, you can then play that game on all supported platforms.
Though it isn't clear how official the poster is, here is another post on a separate EA forum that was edited by an EA employee that states:
The licence is fully transferable - one purchase gets you both the PC and MAC clients
