In addition to proviso to s.115, Rule 73 of Income Tax Rules, 2002 contains the categories of persons who are required to file return electronically. Rule 73 no where says that every business individual has to file return if his income exceeds 5 lacs rupees.
Following sub- rules of Rule 73 are relevant to your query
sub rule (2B)- Every person who is registered for sales tax
sub-rule (2E) - where refund of tax is claimed in a non-company case... income tax return shall be filed electronically.
In addition to above FBR has currently proposed further amendments in the Rule 73 to bring certain other amendments in Rule 73. If these amendments are passed then business individual with turnover of 50 million rupees will have to file return electronically. However, they are not final yet. You may see the draft of proposed amendments at the following link