The purchase of Sun by Oracle for $7.4 billion has far less industry buzz and excitement than the rumored acquisition of Sun by IBM. 

IBM stole the thunder and the impending acquisition of Sun became an imminent and expected event.  While hardware overlap existed in the IBM deal, IBM would have provided a much needed home for Sun's software assets.  Software giant Oracle lacks a hardware portfolio, so the key Oracle / Sun overlaps are far fewer except for the $1 billion acquisition of MySQL by Sun in 2008.  Given Oracle's tendency to be proprietary in its markets, ownership of MySQL by Oracle would be perceived as a great risk in the open source community.

Aside from the unclear direction that MySQL would take under Oracle stewardship, an Oracle / Sun acquisition falls flat for a number of reasons.  The main reason is that Oracle with the partnership of Sun attempted this probable incarnation in 1996 with the introduction of the "Network Computer" (NC).

The notorious and failed NC failed to deliver on promises of complete independence.  After the failed attempt, Oracle went on to acquire a host of independent software companies including PeopleSoft ($10.3 billion), Siebel ($5.8 billion), and BEA ($8.5 billion) without catapulting their shareholder value or creating synergistic value to its customers and the market

Clash of the Titans
The culture of Oracle is broadly and widely known in the industry.  The Sun culture is a close, if not exact fit with the Oracle culture.  Expect a heated clash of hardware mentality vs. software mentality.

Oracle is not a hardware company.  Despite its efforts to be visionary and offer the Network Computer as early as 1996 in a partnership with Sun, Oracle is a software company, more precisely, Oracle is a database company. 

In the IBM / Sun scenario, IBM would know how to protect the Sun hardware assets, integrate Sun's hardware researchers and engineers, and adjust its product offerings to take advantage of the limited but positive market share Sun has in the server market.

Sun is not today, nor has it ever been a software company.  Sun's DNA is hardware-centric and the company does not understand how to develop, productize, and market compelling software.

IBM understands how to productize, develop, and market software.  Granted, IBM's whole rationale behind software is to sell more professional services.  However, IBM has made a commitment to its customers to be more focused on software in the near future.  IBM understands how to take an academic idea and create a product.  This is a skill that Sun has failed on in many instances.  IBM's culture of supreme customer service and eternal customer retention is unique in the industry. 

Oracle, as a steward of Sun's software assets, is far less adept at creating a mass market need for its software.  Oracle tends to focus its software efforts and products on its own platform preservation.

Under Oracle's ownership, the academic assets on Sun's product list, as well as those that may still be in the lab have far less of a chance to succeed because of Oracle's proprietary approach to protecting its platform.  Oracle is not a company that creates software products to enrich the market.  Oracle creates software products to enrich Oracle's proprietary platform and to protect its flagship database revenue.

With IBM, the market would likely have experienced an opportunity to benefit from Sun's software assets.  With an Oracle acquisition, Oracle itself will be the primary beneficiary.

Sun showed us the results of a hardware company's attempt to manage software.  Had Sun fully leveraged and productized its software assets like a true software company, it may not be an acquisition target today.

Software based Oracle runs the risk of significant cost overruns in the hardware business if it is managed like a software company.