I believe the main reason for the delays is because of 3 factors;

1) Since the joining of the newer countries to the EU, there has obviously been a greater amount of people using the EU lane
2) Passengers are now made to wait behind the line & come forward one person at a time, and
3) All passports (with a machine readable strip) & ID cards are now scanned & sometimes may need further scrutinisation due to the increase in forgeries being detected by INS staff