回复：Thanks for all your reasons, let me go deeper...

You posted a very important question regarding Mr' Greenspan's statement. Here is my take to your question.
I think you will agree that a period of 10 to 20 (or 30, many of us have a 30years fixed mortgage) years can be taken as a lone term period.

In early 1980s,the 30 year bond rate reached double-digits (close to 15% in 1981: http://research.stlouisfed.org/fred2/data/GS30.txt)
due to the hyper-inflation (bet most of us were still in China). That was a hyper-inflation period and Mr. Volker boosted the rate so much to combat the inflation successfully.
Then, the 30 year bond rate hit the bottom at 4.5% something after 25 years.You know during this period, the real estate market took off and went up 5-10 folds in various places. This is a once-in-life-time oppotunity.
Now look further for next 25 years. It appears that the trend of the inflation rate (or 30 year bond rate) is set and will follow the exact reverse path what the last 25 years has taken. Or it will move from lower to higher and higher under the background with China, India and many third world countries joining the global capatalism movement.
With this big picture in mind, I tend to agree with Mr's Greenspan statement. The house market will show some up movement but it will be very difficult for it to show the same performance as we have seen during the last 25 years.
If the bond rate really followed that reverse pattern, there would be a lot of oppotunities ahead. However, the real-estate may not be the best vehicle to make you rich (i mean a really rich).