It's All About Feedback
The primary strength of agile techniques is that they reduce the feedback cycle, and thereby the overall cost of software development. Figure 3 maps the effectiveness of agile (shown in green) with the traditional (in red) development techniques, onto the cost-of-change curve. Techniques such as Pair Programming and Modeling with Others have feedback cycles on the order of seconds, whereas test-driven design (TDD) is on the order of minutes and agile model-driven development (AMDD), on the order of hours. Compare these feedback cycles against traditional techniques, such as Reviews or Big Requirements Up Front (BRUF), which have feedback cycles on the order of weeks or months, respectively. I compare the feedback cycles of these techniques, and more, at http://www.ambysoft.com/essays/whyAgileWorksFeedback.html.
Figure 3 is particularly important because it speaks to senior managers. Diagrams like this get their attention, and if the supporting evidence is persuasive, they might consider adopting some of the techniques. The Early Majority, in Figure 1, want to hear about anecdotal evidence; Figure 3 satisfies this need. However, since the Late Majority typically want to see several case studies of firms within their industry before they adopt a new approach, Figure 3 helps them to become more receptive to agile techniques. The Laggards want incontrovertible proof before trying something new: I suspect they'll still be sitting on the sidelines for a few more years.
My prediction is that in the next few years, we'll see agile techniques and even full-scale methodologies adopted within the Early and Late Majority organizations, and even among some of the Laggards. Although the current boutique consulting firms specializing in agile software process improvement will continue to thrive, we'll see a shift within the industry towards large, traditional consulting organizations (like Accenture or IBM Global Services) that have traditionally had the ears of senior IT management. Agile software development is clearly crossing the chasm, and so must the innovators within the agile community.