Ramit Sethi[1] focuses almost exclusively on increasing income. He thinks the "latte factor" is bullshit, since you can just bring in more money.
Personally, I think that increasing income and reducing expenses are two sides of the same coin. You're either changing the numerator or the denominator in the time-to-FI equation. The really powerful stuff happens when you do both at the same time.
Perhaps you know the math, but I think it is important to be clear to readers that a penny earned is LESS than a penny saved.
Put another way, are making $10,000 more dollars per year and spending $10,000 less per year the same? No. You will retire exponentially (literally, if not colloquially) sooner by spending less.
Personally, I think that increasing income and reducing expenses are two sides of the same coin. You're either changing the numerator or the denominator in the time-to-FI equation. The really powerful stuff happens when you do both at the same time.
[1]: http://www.iwillteachyoutoberich.com