I don't remember who ever said a resume should be one page. This statement was probably uttered before I ever started recruiting by a lazy recruiter that didn't like to turn pages (did I just say that out loud?). This was adopted as conventional wisdom by the masses. Aside from the fact that the statement is just wrong in my opinion (I'm not that into cookie cutter advice...most advice may work for most people but one size does not fit all), it won't work today. Times have changed and the one page resume is a thing of the past (with one exception and that is the relatively new graduate).
Here's what's led to the demise of the one-pager:
Employees no longer have the same kind of employer loyalty that they did in the past. OK, wait a sec, before you get upset and explain how loyal you are to your employer. It's just changed. My grandfather worked for 2 companies for his whole career and they gave him a pension (remember those?). Talk to someone today who has worked for only 2 companies and they are either a few years out of school or they are worried that their long tenure at so few companies is seen as a red flag by hiring companies.
A few things have caused this. Most companies have done away with pensions and many have started giving stock options. Because of the dynamic nature of the stock market, people are more willing to cut bait and leave some stock on the table. Companies can't compete based on stock alone. They also have to compete on scope of work, culture, career paths and other things. Second is the concept of the employment marketplace. Years ago, if you wanted to change jobs, you put on a suit and walked into the "Personnel" office (remember when they called it that?) of another company to apply. Today, it takes just the click of a mouse. You can apply for hundreds of positions online in a single day (not that I wold necessarily recommend that) and the internet enables you to view the employment offerings of any given company in detail. As a result, employees are more empowered to drive career change. Candidates have more choices and more power in the marketplace and now see their relationship with their employer as more of a deal than a commitment. You stay with your employer as long as you are getting a good deal. These things have led to a point where a person is expected to work for a number of companies over the span of a career. Hardly something you can fit on that one page resume, right?
You can also see how companies have changed the way they hire and the impact that has had on peoples resumes. Frankly, the staffing industry got smart. Companies are now understanding the huge cost associated not only with turnover in a specific role, but with company turnover. They started to look at what an "ideal" company employee looks like..the types of skills and talents required to be successful in their workplace. By doing this, companies have enabled employees to build careers by identifying a succession of different roles within the same company (the stigma of multiple job changes may be gone, but many people like the variety of changing jobs without the pain of changing companies). Companies keep their good employees by helping them move into different roles in their organizations. Employees stay engaged and interested because they are being offered interesting work. All of these role changes need to be documented on a resume and again, the one pager just isn't going to work.
So looking at job seekers who have worked in a multitude of roles within one company or have moved around a bit because of the change in employment market climate (or a combo of both), you can see that documenting experience gathered along the way has become more complex. And it just won't fit into a one page resume. Keeping in mind that a resume is really just a teaser...enough to get a phone call from a recruiter but not intended to document ALL of your experience, I am not suggesting that resumes should be expanded to more than 3 or 4 pages. Just don't feel like you have to fit it all onto one page. I, for one, don't mind turning pages.