It's not just mining. The general trend over time is centralisation of everything. That's because professionalism is important but takes a lot of work, and the most obvious way to fund it is through offering services and charging a fee. Right now for a lot of Bitcoin users, their experience is like:

- Buy some coins on coinbase (essentially a bitcoin bank)
- Send them to a friend who uses blockchain.info
- Mine on a big pool like BTC Guild or GHash.io
- From time to time, buy things from a merchant who is using BitPay

It varies by region of course. Here in Europe I see a lot of people using the Android SPV wallet, so that's at least fairly decentralised. But it takes huge and constant effort to keep the decentralised solutions competitive with the more centralised forms. Cracking that problem is something I've spent a lot of time thinking about.