Comcast Up, Blockbuster Off Before Bell  NEW YORK (Reuters) - Shares of 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; rose  2 percent before the bell on Wednesday after the largest U.S.  cable operator posted a quarterly profit below Wall Street  estimates but reported better-than-expected gains in high-speed  Internet customers.