Comcast Posts Profit, Gains Customers  NEW YORK (Reuters) - Comcast Corp. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=CMCSA.O target=/stocks/quickinfo/fullquote"&gt;CMCSA.O&lt;/A&gt;, the largest  U.S. cable operator, on Wednesday posted a third quarter profit  on better-than-expected gains in high-speed Internet customers  and raised its full-year outlook for subscriber growth.