I always consider weaker students. If a student is weaker - they need a different text for self study, and targeted guidance in guided study. This is where the inquirey approach to learning and teaching comes in.
http://nzcurriculum.tki.org.nz/Curr...chers-as-learners-Inquiry/Teaching-as-inquiry
Profs usually give answers to exercises because that is where the assessment will be based: students need to understand what they need to do to get the marks. This is somewhat different from providing an exercise to learn maths or physics.
Sometimes it is because the profs are not trained educators so do not really know what they are doing or they are just copying how they were taught, sometimes because they prefer a different teaching style to Hassini.
Personally, when I provide model answers, I include some errors - encouraging students to question what they are told. For similar reasons, I break with my colleagues by never giving a mark for the final number in long-answers: just getting the right answer does not get any marks. Marks are awarded for evidence of behaviours I want to encourage. When it comes to help for text exercizes, I would provide related but scaffolded exercises in a separate sheet.
Of course, a solo student, having bought this text by mistake, may rescue the situation without undue expense by referring to a list of answers ... what a lot of texts at Hassini's level do is put answers to every other problem for much this sort of reason. The student is still better off looking to a different resource.
Even so: it is impossible to cater to every student in one book or in one class: some students are, justly, going to fail the course.
I'm not saying "never to give answers to exercises", just that Hassini has deliberately withheld the answers
for a reason. We should be careful not to defeat the purpose. We should also bear in mind that a lot of profs will set assignments from this kind of textbook...