The difference is easy to understand. I will explain what's the difference.
Standard Trade.com account uses ECN execution. It's as you may know, direct execution on market, brokerage is just intermediary. DMA is the same - brokerage gives you direct market access? So why choose DMA?
The thing is, that ECN-execution is excution by liquidity pools. The brokerage uses gathered liquidity pool, gathered by liquidity provider to its traders. ECN execution. as you know, sometimes faces with re-quotes, when another side, abandones the order or execute it just partially. Also, ECN brokers have no agreements with each of liquidity providers, the more providers, the higher comissions or spreads.
DMA is a kind of direct market execution, however, the brokerage has an agreement with each liquidity provider directly, the brokerage that offers DMA quotes and execution offers its traders the pure quotes, provided by each liquidity provider, the spread for DMA account consists of liquidity provider-spread and mark-up, a profit for brokerage. Of course, DMA is harder to develop and offer, as it requires signing agreemets with different liquidity providers, so brokers usually set min deposit starting at $10,00-$20,000. Hulas says that Trade.com has extremly high min depo for DMA accs, I can't agree, compared to other brokers, that's even lower.