The Power of $$$
-MUCHO DINERO. All my friends who did industrial internships made WAY more than I did in my academic internships (namely REUs). REUs typically pay anywhere from $3000-5000 depending on where it is and depending on whether they give you money for an apartment/dorm or not. (If you guys wanna know about my personal experience with money, I can give a complete reportlater). Now, let us compare my friends who worked at P&G, Albemarle, and other companies. They made $10,000 + housing allowances for the same amount of work I did. Actually, it wasnt even the same amount of work. I worked around 50-60 hours a week, while they worked 40. Gah...
The Power of Connections
-There's a big difference here. This is where academic internships are WAY better than industrial ones (unless your industrial one is connected to academic research, then you can have the best of both worlds). With REUs, you interact with professors, i.e. experts in field. I know that my REU letters of rec got me into several schools (it was even cited in my letter), and so impressing those people are really good since they can have pull on admissions committees. Now, letters of recommendation from industry dont have as much pull typically because the admissions committee doesnt know the person. Dont let this make you slack though. If you sucked ass in a academic REU but rocked in an industrial, your letter from industry will be better even if they dont know the person.
The Power of Publications
-Again, another big difference. Industry is typically secretive, and unless you're INCREDIBLY lucky, your work will only be published in an internal company report. You cant exactly cite that due to IP laws and agreements they typically make you sign. Now, look at academic internships where more than likely, you'll end up co-authoring something. Publications = big deal in grad school applications.
And that's pretty much it. It all comes down to do you want a lot of money for the summer, or do you want to experience graduate school lifestyle (including the underpaid-ness) of it all. I leave that up to you.