Considering the cost of comics today and their ever-fluctuating price points, page counts, and formats, it's hard to imagine a hike of two pennies causing much concern. But consider the situation DC and the rest of the American industry found itself in by the time this increase finally did come to pass: comics had a standard price of 10 cents from their beginnings in the mid-1930s up until late-1961 — over 25 years.
And over that time, the width of a standard-sized comic had narrowed, and page counts had gradually dropped from 64 pages, finally to 32 pages — so that by the mid-1950s, the standard comic format had come to look much like the standard comic format does today.
A few years after that, printing economics dictated that the format would shrink no more, and the industry finally bumped prices up from 10 cents to 12 cents. Both Marvel and DC made the move over the fall/winter 1961 period.
A couple months later, DC felt it necessary to explain to readers what had happened. Here's the editorial that ran on inside front covers, this particular pic from Mystery In Space #73 (where any reader anger may have been somewhat mollified by the first appearance of Adam Strange).
You've gotta love that closer: "We feel confident that you understand the necessity for this slight adjustment, and will remain our loyal fans."
Thanks to ivegotneatstuff on the Collector's Society forum for the great pic.