Marketo could have been too expensive for Salesforce.com to buy, said analyst Ray Wang, CEO of Constellation Research.
Meanwhile, it's not clear how Salesforce.com's existing relationships with Marketo and other marketing software partners will change moving forward.
Salesforce.com's AppExchange, where partners can showcase their products, is "a dynamic marketplace," Benioff said during the call. "People are constantly coming and going. We understand that and you can see how it changes and evolves over time."
"We certainly plan to continue to support all of our partners in the AppExchange," Salesforce.com chief operating officer George Hu said in an interview. "We've always had an open philosophy."
However, Salesforce.com's ability to offer a unified marketing platform will result in many customers making the switch from other marketing products, Hu added. "We think customers are going to be very excited about it."
Hu declined to say whether Salesforce.com had considered buying other companies besides ExactTarget. "This is the company we've been focusing on for a while now."
While it may be surprising that Salesforce.com waited until now to buy a company like ExactTarget, it had its reasons, according to Hu. "We have been learning a lot about CMOs in the last few years," he said.
Salesforce.com's previous acquisitions of Buddy Media and Radian6 provided "a huge catalyst" for the ExactTarget deal, he added. "We had many deeper conversations with the CMO that gave us the education and understanding of the market that allowed us to move forward with such confidence."
Overall, Salesforce.com will be "in co-opetition with Marketo and all other marketing automation products," but the stakes will vary depending on the situation, Wang said.
As a whole, Salesforce.com's Marketing Cloud product family "plays a central role as an aggregator for the CMO," he added. "So if you are very specialized in marketing analytics, it's not an issue. If you are doing core marketing automation and campaign management, you are in direct competition."
But one observer questioned whether Salesforce.com is overpaying for ExactTarget.
"I look at this and I shake my head," said analyst Denis Pombriant, managing principal of Beagle Research. "ExactTarget has done a great job over the years of expanding its offering. But I just question the $2.5 billion, that's a huge amount of money for something like this. A company like Salesforce could have built this."