There are differences:

• The investor presentation contains more content than a sales presentation: financials, strategy, etc.
• The investor presentation makes a competitive comparison explicit, while usually in a sales presentation you state your competitive advantage without explicitly mentioning competitor names and their strengths and weaknesses
• A (summary of) the sales presentation should be embedded in the investor presentation to convince the investor that you can sell your product today (she will look at the content of the slides, but also - more importantly - how good a job you do at selling the product)
• Sales presentations are often too "deep in the trenches" for the big picture investor presentation. Tactical and operational issues are addressed that are very important to close that deal, but add less to the investor pitch 
• Sales presentations are usually geared towards bigger customers (that merit a customised approach) and do not address self service sales to smaller customers (that could be an equally big, or even bigger part of your business).
• Sales presentations talk about customer issues today, outside the context of a longer-term roadmap for the company.

Art: a recent painting by Andrew Stevovich, check out his blog, it has detailed backgrounds on how he creates his artwork.