I guess it all depends where you are in Europe and what ISP you have. I don't know about Spain but I think France, Belgium, the Netherlands , (Germany) have very good cable infrastructure and ADSL is available almost in every city. In the UK which has a better tax situation, it appears to be a bit patchy, ADSL is available almost everywhere through dozens of ISP's but cable only in a few areas., but ADSL speed is always 512K. I had a tough time finding cable in London and my connection here is THE worst POS I have ever had, last year when I was in the South East on cable and it was almost flawless with different throughput from 128K to 600K. Still on the continent cable is at 1Mbps, even 3Mbps + at the same cost. Now that doesn't make a lot of difference in real life. But it helps if you are not a frigging scalper.
And to answer your question , you certainly do not need a T1 line if you get a reliable and fast connection which you should get if you opt for cable. The delay is insignificant then , I used to daytrade eminis on cable and always got the price I saw on my quotes, at worse one tick slippage.