actually there is no big differences between s270 and z7. The differences are structural. S270 has a adjustable shoulder strap and z1 has not nothing like that. S270 can record 4 channel audio, on the other hand z7 has two channels for recording the audio. S270 supports and can record on Standard DVCAM 184 m cassettes but z7 only support minidv/hdv cassettes.
but all the operational features of the both cameras are same. but i found z7 more comfortable for shooting.