Great question bhat.  No, your domain can't be purchased by others.  This service "Premium Domains", or Backorder Domains is referring to back ordering a domain.  Anyone can buy the rights to an existing domain in hopes of acquiring it if the domain ever expires.  You typically pay a fee for the domain and then the service will check it regularly.  If it ever expires and is released the service automatically registers the domain name for you and sends you the info.  This is not to be confused with another type of "Premium Domain" service which is buying existing domains that are registered but listed for sale by owner at a much higher price then unregistered domains.  These domains are often very valuable and owned by someone that lists them for sale on a Premium Domain website.