Not true. Sena has the exact same warranty that Scala has. Like all major manufacturers do.
Look at the last box on this page http://www.sena.com/support/warranty/
Here's the quote:
Important Message to Customers in the US and Canada
Buying from unauthorized dealers can be risky. The products purchased from unauthorized dealers may be counterfeit, stolen goods or second hand products, which will not be covered by warranty. The only way to be sure you're buying a genuine and legitimate product is to buy from an Authorized Sena Dealer or Sena directly. To see the list of Sena Authorized Dealers in North America, please click here.
* Note about eBay/Craigslist:
Many resellers who sell through eBay and Craigslist are not authorized resellers. When purchasing, it is important to note where the product is being shipped from and sold by. Please refer to the Sena Authorized Dealer list or contact us directly before you purchase, if you are uncertain.