No. It isn't.
Facebook does some things really well, and others it doesn't do at all.
Here are a few more reasons why Facebook just isn't enough for your small business:
1. Facebook is a huge marketplace, and your competitors may have paid advertisements appearing on your own page. You don't have full control over how your page appears to your customers and it could end up driving them toward the competition.
2. Your fans may very rarely see your updates due to the flood of updates in their timeline and Facebook's own algorithms which determine what appears and what doesn't. In fact, some companies have found that as few as 1% of their posts appeared on their timelines.
3. Google+ can actually affect search engine optimization (SEO). Even if Google+ competes with the likes of Facebook and Twitter, it still plays an important role by showing up in search results.
4. The younger generation is trending away from Facebook - don't miss out on these customers simply because you've put all your 'internet-eggs' in the Facebook basket.
5. Facebook is full of distractions, your website isn't. If your customers are on Facebook, then your company is competing with all of their friends, their other favorite businesses, chats, photos, videos, and advertisements, all drawing their attention away from what you want them to focus on, your brand.
So keep the Facebook page if you have one, and if you don't, make one - there are still 757 million daily active users of the service. But don't let it be the sole means for your customers to find your company and see your message.