What did Del Webb do right?

Can't be all blind luck.  Del Webb did not follow reasonable construction procedures...but nothing bad happened?  How come?

First off note that a lot of this is conjecture.  Intelligent conjecture...but conjecture none the less.  It would require a very large sum to find any truth in this matter...and the concerned parties seek advantage rather than truth. 

Well Let's start by looking at what is thought to cause stucco problems.  From the Woodbury site:

Q. What causes the problems?

(We have struck out those unlikely in Sun City Summerlin. )

A. Window leaks are the cause of the majority of the damage but the causes may be many, including:

• The paper around windows and other openings was installed incorrectly.
• Head flashing was not used on windows (windows with flanges were thought to be self-flashed).
• One layer of paper was used. Water may be leaking through the paper.
• The windows themselves leak.
• Kickout flashing was not installed at the wall/roof intersections where the roofline does not extend below the wall.
• The deck ledger board was not flashed.
• Moisture from rain during construction or wet building materials remain in the wall (construction moisture).
• Interior moisture is permeating into the wall.
• Lack of drying capacity. All walls will likely leak sometime during their life. In addition condensation and construction moisture will be in the walls. Stucco walls are very tight and cannot withstand much moisture without creating mold and rot.
• Solar drive may be pushing moisture from a wet stucco wall into the wall cavity.
• Type 15 felt may be acting as a vapor retarder trapping moisture in the wall.
• Oriented strand board (OSB) sheathing has a low perm rating and it may be acting as a vapor retarder creating a double vapor retarder situation. In addition OSB absorbs and retains moisture making it vulnerable to mold and rot.
• The staples that stick through the sheathing are collecting frost or condensation and dripping within the wall cavity.
• The high number of staples used to fasten the lath creates many penetrations that could both leak and condense moisture.
• The staples were driven into the lath with excessive force causing the lath to cut the paper creating a leak.
• Wind driven water is getting on the wall through the soffit vents and running down the wall between the sheathing and the paper.
• Weep screeds were not used at the bottom of the stucco. This may prevent trapped water from draining.
• Stucco was installed below ground. This may prevent trapped water from draining or may wick water up to the framing. In addition, when stucco is applied below grade there is no clear definition of where grade should be and often the grade is placed against the wood framing causing a guaranteed rot situation.
• Stucco is installed directly on the foundation without paper or a weep screed. This prevents trapped water from draining.
• Landscape trees or bushes that contact the stucco create an area that introduces and holds moisture in the stucco. The moisture permeates into the wall.

Perhaps stated positively....

• Ain't much rain.  And when it does rain it is generally followed by periods of very strong drying.
• Del Webb did a reasonable job on the windows.  They are well sealed and generally don't leak.
• The homes have roofs with a high  overlap over the walls. The roof extends well out to keep out the sun  This also protects the stucco from rain.
• The ground into which the stucco extends is generally dry.  So it tends to wick moisture out of the structure rather than into it. 
• No or very little trapped water... So no need for an outlet for it.
• Landscaping in general does not provide moisture to the walls.  It is distant from the stucco and the grade slopes away from the home. Much of this below ground stucco terminates in dry gravel. 

Summarizing - In this climate Del Webb did enough correctly that stucco water damage is not a wide spread problem. 

So it is not a problem?