The verb use of concept is not new; examples are known dating back to the early 1980s (and some of these examples imply that the term was well-established even then). However, it seems not to be especially common, even within its industry. For example, Adweek has used concepted or concepting only 12 times since 2003. (I searched for the inflected forms to distinguish the verb from the noun.) That's not nothing, but on average you could read the magazine weekly for three months before you'd find a single example; compare this to the 405 examples of creatives the magazine printed in the same period. (The noun creative referring to "a person who does creative work, esp. in advertising" is more than 50 years old and universally used in the industry, though often thought to be unusual by outsiders.)
Furthermore, established industry figures themselves deny that concept is a commonly used or accepted verb. One senior director, who writes a column in an advertising magazine, told me: "This is not true advertising jargon—it's something maybe used by a sub-subset of young creative people talking among themselves. It marks you as a philistine." A senior partner at a big-name firm said he found it "jarringly odd," adding that "if anyone on my team said it in a client meeting, I wouldn't fire them, but I would pull them aside and tell them, 'That is not English.' "
So, the problem here isn't that Merriam-Webster is keeping concept out of the dictionary because they're mean or because they have no respect for the creative process. It's that Del Savio is just too early; the word isn't ready yet. When it is, it'll get put in, the same way that the noun creative is already in Merriam-Webster's Collegiate Dictionary—and the Oxford English Dictionary, and the American Heritage Dictionary of the English Language, and others. The best thing Del Savio can do to help concept's chances is not to blog about it but to spend more time doing his job. That way maybe he'll become influential enough to get other people to use the term. Then it will be a no-brainer.
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Correction, May 18, 2006: This piece originally misspelled the name of copywriter Ray Del Savio.