Sure, if your market lets you charge more, go ahead and charge more. But in some markets, real businesses charge $5/mo, because market conditions don't let them charge $10/mo (or at least don't allow them to meet their other goals at that price). Evernote Premium is $5/mo, Google Drive charges $4.99/mo for 100GB of space, etc. Heck, Fastmail charges $1.65/mo for its "Full" plan (billed as $20/yr), or $3.33 for its "Enhanced".