Increasingly businesses are seeing the power of decentralizing their businesses so that expensive large monolithic central offices will no longer be required. We have the pieces coming into place, secure remote access to business locations, instant communication in the form of cell/IM/conferencing, pending high bandwidth pipes (FTTP) to people's homes and nearly ubiquitous wireless access and increasingly electronically run business processes in all types of businesses.
All these factors when fully employed in the business world will mean a much lower need for physical office locations and workers AT those locations, which means cut costs on maintaining such properties, paying rent, paying utilities and hiring repair and maintenance folks.
This means vast reductions in commuting workers and reduced electrical demand at least over small regions (you'll still increase it over the larger metropolitan area but larger areas tend to be serviced by multiple power grids, reducing the likelyhood of peak collapse for the collection.) 10 years ago the birth of the purely internet driven business inspired the concept of businesses mostly run online, this allowed the early players to rapidly become revenue competitive with their brick and mortar counter parts.
However traditional brick and mortar businesses had not begun to move in the opposite direction (toward the internet model) the continued rise of the distributed internet business in the form of web services/SOA/ssl VPN driven initiatives will make the need for big office towers significantly reduced. Even as businesses grow in employees the need to provide physical locations for those employees will dwindle and I predict essentially disappear. (Imagine the day you go for an interview and a prerequisite of the job is that you work from home but that you dont' have to worry about having a pc and pda, the company will provide it FOR you.)
There will be a time when the top brass of businesses actually come to work (ironically) more often than the lesser employees, everyone else will be mandated to work from home all or part of the time to save money. (Such people will alternately share an office or cubicles when coming in to further save money.) So in response to the pure internet players of a decade ago who showed that corporations could thrive without huge investments in physical offices, brick and mortar companies will move slowly to be less brick and mortar and more pure from an internet perspective.
Of course there will be exceptions to this trend, companies that require the physical presence of people (manufacturing, utilities, construction, human services, food,dry cleaning..etc.) will continue on with their marginal growth curves (relative to what is predicted for knowledge workers) but I don't think they will change the outcome as the city has been on a downward spiral for such jobs for decades now.
I think existing brick and mortar businesses are going to see this change over to a telepresent work force as viable and cost effective within the next 5 - 10 years, the transition being facilitated by increased broadband penetration to homes and the aforementioned building of agile secure distributed business systems that do not require physical presence for knowledge workers to do their jobs.
(Edit: 3/14/2008 Businesses starting out today can already take advantage of these economies if they have the facilitating software to ensure every aspect of business can be managed and performed in a secure and distributed fashion. Collaboration needs to be integrated with workflow in currently non commercialized ways to open up a new category of hyper efficient run businesses. )
What does this have to do with NYC growth? Well , the window for the predicted choking of our city on people is well beyond 10 years time, for the reasons mentioned I don't think as many people (those that currently commute to work) will need to live IN the city as the projections in the article indicate. I assume (without data to support the claim) that most workers in the city are indeed knowledge workers as opposed to people that prepare goods for sale or who's physical presence is required for rendering a service. Knowledge workers will simply need to have access TO the city and it's businesses and that will become increasingly possible for the reasons described before.
Still there are people that need to come to the city, those that keep the city (first responders, utilities, infrastructure supporters) these people will use the infrastructure regularly but the growth in their numbers will be tied to the size of the city and if businesses aren't building any more towers , there will be a reduced need for the city to provide the infrastructure conduits to get the people that man the towers to the towers.