UK Immigration is trying to reduce levels of overall immigration into the UK. Recently the UK Immigration Minister Damian Green has been expressing concerns about the number of students on student visas in the UK.
It seems quite likely that in future it will either become more difficult to come under the Tier 1 PSW visa or it will end altogether. This will mean that far fewer people on Tier 4 student visas will be able to stay in the UK in the longer term.
The Tier 1 PSW visa was brought in by the previous Labour Government to enable students to remain in the UK to work and possibly qualify in future for longer term visas such as the highly skilled Tier 1 (General) visa or Tier 2 work visa. To qualify for the Tier 1 (General) visa you need to have recent work experience. Students who have studied in the UK for some years on a degree are unlikely to be able to qualify for the Tier 1 (General) visa unless they have the opportunity to gain additional work experience under Tier 1 PSW. Because of the UK immigration quota and other changes it is also more difficult to come under Tier 2 (General).