For the Nth time, you can use a broker to avoid paying the 30BTC registration fee. Do you also refuse to trade stocks listed on the NYSE because you don't want to pay the $1M (currently about 1750 BTC) it would cost to get a seat on that exchange?
Let's compare MPEX to the NYSE.
Age: 2 years vs ~200 years.
Market Cap*: $240,000 vs $16,000,000,000,000
Yearly trading volume*: Less than $100,000 vs more than $20,000,000,000,000
Number of listings*: 1 vs 1875
Number of seats: ~1000 and counting vs 1366
Price for a seat: $18,000 (7% of market cap) vs ~$1,000,000 (0.000006%)
Determining seat price: arbitrary vs supply/demand
Reward for convincing someone to buy a seat: $6,000 vs $0
Requires a seat to trade directly on the exchange: Yes vs no
Brokers: Some guy who set up a website in an afternoon vs several multibillion dollar financial institutions.
*excludes stocks MP/NYSE created/owns.