I find only one difference going to Sequential file, In VSAM sequential files are of ESDS-Entry Sequential Data Sets:
In which Random Accessing is possible by RBA(Relative Byte Address).
which a general sequential file doesn't have.
if you get any more differrences, plz let me know it.
You can create files in Non- VSAM entries also using QSAM, BDAM and ISAM. But files created with VSAM (ESDS, RRDS, KSDS) are more sequired, independent and can be accessed faster comparing non-vsam files.